Cell-Like Movement on a 2D Simulation: How to stop erratic movement and add colliders

Hello, I'm a total begginer in coding and game-making, but I adventured myself in trying to produce a cell-like simulation, where the red cells chase and eat the green ones, who try to escape. I can show you the code, and you can try for yourself. But I have big issues here, and I just don't know how to solve them.

1) The cells have an erratic movement, since their position is updated and changed every frame. For example, in frame 1 I tell them to move 10 units up, but on frame 2 I change that value to -10, and so on, so they are constantly shifting and changing direction. Altough this is kinda like a real cell movement, I would like to have controll over this.

2) The code is a mess. I didn't knew how to make them leave the corners, so I made some pseudo-coding. It's the definition of "If it is stupid and it works, it ain't stupid." The thing is: they still get stuck in the corners sometimes, so I'm thinking that there's got to be a way to make this behaviour easier.

3) Finally, if I have 2 green cells, even tough they have Circle Colider 2D on each one, they still go over each other. This should be fairly simple to fix, but I don't know how.

 using UnityEngine;
 using System.Collections;
 
 public class Mover : MonoBehaviour {
 
     public GameObject[] enemies;
     public float walking;
     public float speed;
     public float detectionRadius;
     public enum State {chasing, running};
     public State stateIs;
 
     private GameObject closestEnemy;
     private float dist = Mathf.Infinity;
     private float runningX;
     private float runningY;
     private string corner;
     
     void Update() {
         float thisX = this.transform.position.x;
         float thisY = this.transform.position.y;
         FindNearest ();
         if (this.stateIs == State.chasing) {
             Vector3 increase = new Vector3 (closestEnemy.transform.position.x,
                                             closestEnemy.transform.position.y,
                                             closestEnemy.transform.position.z);
             this.transform.position = Vector3.MoveTowards (this.transform.position, increase, speed);
         }
 
         if (this.stateIs == State.running) {
             if (thisX < 8.5) {
                 if (thisY < 5) {
                     Debug.Log ("UnStucking Bottom Left");
                     Stuck ("leftBottom");
                 } else if (thisY > 10) {
                     Stuck ("leftTop");
                     //Debug.Log ("UnStucking Top Left");
                 } else {
                     Decision ();
                 }
             }
             else if (thisX > 21.5) {
                 if (thisY < 6.5) {
                     Stuck ("rightBottom");
                     //Debug.Log ("UnStucking Bottom Right");
                 } else if (thisY > 10) {
                     Stuck ("rightTop");
                     //Debug.Log ("UnStucking Top Right");
                 } else {
                     Decision ();
                 }
             }
             else {
                 Decision ();
             }
         }
     }
 
     void Decision() {
         float dist = (this.transform.position - closestEnemy.transform.position).sqrMagnitude;
         if (dist > detectionRadius) {
             Idle ();
             Debug.Log ("Idle");
         } else {
             Run ();
             Debug.Log ("Run");
         }
     }
 
     void Run() {
 
         float thisX = this.transform.position.x;
         float thisY = this.transform.position.y;
         FindNearest ();
         
         if (closestEnemy.transform.position.x < thisX && thisX < 22) {
             runningX = this.transform.position.x + 1;
         } else if (closestEnemy.transform.position.x > thisX && thisX > 7.7) {
             runningX = this.transform.position.x - 1;
         }
         
         if (closestEnemy.transform.position.y < thisY && thisY < 11.5) {
             runningY = this.transform.position.y + 1;
         } else if (closestEnemy.transform.position.y > thisY && thisY > 5){
             runningY = this.transform.position.y - 1;
         }
         Vector3 increase = new Vector3 (runningX, runningY, 0.0f);
         this.transform.position = Vector3.MoveTowards (this.transform.position, increase, speed);
     }
 
     void Stuck(string corner) {
         if (corner == "leftBottom") {
             float thisX = this.transform.position.x;
             float thisY = this.transform.position.y;
             runningX = thisX + Random.Range(10f,17f);
             runningY = thisY + Random.Range(10f,17f);
             Vector3 increase = new Vector3 (runningX,runningY,0.0f);
             this.transform.position = Vector3.MoveTowards (this.transform.position, increase, speed);
             }
         else if (corner == "leftTop") {
             float thisX = this.transform.position.x;
             float thisY = this.transform.position.y;
             runningX = thisX + Random.Range(10f,17f);
             runningY = thisY - Random.Range(10f,17f);
             Vector3 increase = new Vector3 (runningX,runningY,0.0f);
             this.transform.position = Vector3.MoveTowards (this.transform.position, increase, speed);
             }
         else if (corner == "rightBottom") {
             float thisX = this.transform.position.x;
             float thisY = this.transform.position.y;
             runningX = thisX - Random.Range(1f,7f);
             runningY = thisY + Random.Range(1f,7f);
             Vector3 increase = new Vector3 (runningX,runningY,0.0f);
             this.transform.position = Vector3.MoveTowards (this.transform.position, increase, speed);
         }
         else if (corner == "rightTop") {
             float thisX = this.transform.position.x;
             float thisY = this.transform.position.y;
             runningX = thisX - Random.Range(1f,7f);
             runningY = thisY - Random.Range(1f,7f);
             Vector3 increase = new Vector3 (runningX,runningY,0.0f);
             this.transform.position = Vector3.MoveTowards (this.transform.position, increase, speed);
         }
     }
 
     void FindNearest() {
 
         float closestDist = Mathf.Infinity;
 
         foreach (GameObject enemy in enemies) { 
             float dist = (this.transform.position - enemy.transform.position).sqrMagnitude; 
             if (dist < closestDist) { 
                 closestDist = dist; 
                 closestEnemy = enemy; 
             } 
         } 
     }
 
     void Idle() {
         float thisX = this.transform.position.x;
         float thisY = this.transform.position.y;
         //isCenter
         if (thisX < 22 && thisX > 8 && thisY < 11.5 && thisY > 4) {
             runningX = this.transform.position.x + Random.Range (-1.0f, 1.0f);
             runningY = this.transform.position.y + Random.Range (-1.0f, 1.0f);
         } 
         //MoveToCenter
         //isBottom
         else if (thisY < 4) {
             runningX = this.transform.position.x + Random.Range (-1.0f, 1.0f);
             runningY = this.transform.position.y + 5;
         }
         //isTop
         else if (thisY > 11.5) {
             runningX = this.transform.position.x + Random.Range (-1.0f, 1.0f);
             runningY = this.transform.position.y - 5;
         } 
         //isLeft
         else if (thisX < 8) {
             runningX = this.transform.position.x + 5;
             runningY = this.transform.position.y + Random.Range (-1.0f, 1.0f);
         } 
         //isRight
         else if (thisX > 22) {
             runningX = this.transform.position.x - 5;
             runningY = this.transform.position.y + Random.Range (-1.0f, 1.0f);
         } 
         //Debug.Log ("Moving " + runningX + " units horizontal.");
         //Debug.Log ("Moving " + runningY + " units vertical.");
         Vector3 increase = new Vector3 (runningX, runningY, 0.0f);
         this.transform.position = Vector3.MoveTowards (this.transform.position, increase, speed);
     }
 }