Blend textures in shader

Hi all;

I'm trying to blend three textures without much success. This is what I have at the moment:

 Shader "Custom/somethingElseElse"
 {
     Properties
     { // two textures
     _tex0 ("Texture1", 2D) = "white" {} // snow
     _tex1 ("Texture2", 2D) = "white" {} // rock
     _tex2 ("Texture3", 2D) = "white" {} // grass
     
     }
  
     SubShader
     {
        Tags {Queue = Geometry} // default for unity, opaque
        ZWrite Off // turn off as we are drawing a semi-transparent object
        Lighting Off // turn off surface lighting
        Pass // do this in one draw call
        {
        CGPROGRAM
             // default for unity, basic shader model 2.0
          #pragma target 2.0 
          // vertex program vert provided for use
          #pragma vertex vert
          // fragment program frag provided for use
          #pragma fragment frag
          // enable use of many cg helper functions
          #include "UnityCG.cginc"
  
          sampler2D _tex0; // enable properties for a 2d texture
          sampler2D _tex1; // enable properties for a 2d texture
           sampler2D _tex2;
  
           // call the struct that takes data from vertex to fragment - v2f
          struct v2f 
          {
           float4 pos : POSITION;
           float4 color : COLOR0; // first colour 
           float4 fragPos : COLOR1; // 2nd colour
           float2  uv : TEXCOORD0; // first UV coordinate
          };
  
          float4 _tex0_ST; // get tiling/offset info of tex0
  
           // takes a appdata_base called v and returns a v2f struct called vert
          v2f vert (appdata_base v) // appdata_base is a vertex holding pos, normal and one texture coordinate
          {
           v2f o;
           o.pos = mul (UNITY_MATRIX_MVP, v.vertex); // UNITY_MATRIX_MVP - current model*view*projection matrix
           o.fragPos = o.pos;
           o.uv = TRANSFORM_TEX (v.texcoord, _tex0); // TRANSFORM_TEX - part of UnityCG.cginc,  make sure texture scale&offset is applied ok
           o.color = float4 (1.0, 1.0, 1.0, 1);
           return o;
          }
  
          half4 frag (v2f i) : COLOR
          {
           float2 q = i.uv.xy / float2(1,1);
           float3 oricol = tex2D (_tex0,float2(q.x,q.y)).xyz;
           float3 col = tex2D (_tex1,float2(i.uv.x,i.uv.y)).xyz;
           float3 othercol = tex2D (_tex2,float2(q.x*0.5,q.y*0.5)).xyz; // third texture
           float comp = smoothstep( 0.1, 0.9, sin(0.5) ); // Interpolate between 0.2 and 0.7 with smoothing at intervals sin(0.5) - default 0.2, 0.7
           col = lerp(col,oricol, clamp(-2.0+2.0*q.y+3.0*comp,0.0,1.0)); // start mixing between min and max - lerp and clamp
           return float4(col,1);
          }
        ENDCG
        }
     }
     FallBack "VertexLit" // default failsafe shader to use
 }

I've managed to blend two textures so far, however whilst trying to add another texture - grass in my case, I don't know what to do as the lerp function i'm using is unable to accept another float parameter (othercol in my case). I have a plane that currently has a material with 3 textures assigned - snow, rock and grass, in which I'm hoping to blend between them smoothly (snow > rock > grass)

I would appreciate any advise on how to tackle this problem. Thank you