Sprite in 3D environment with lights problem

So hey, I'm trying to create something like good old Doom shooter, with sprites and all that old stuff, but with good lighting. And because of lighting came up first problems. Check this picture:

So first problem is like shadow from background guy visible on the front side of the near-to-camera guy. Can I remove that shadow and make it visible only from behind? Like it do on real 3D objects? I'm tried edit sprite shader and added Cull Back, but then sprite itself doesn't cast shadow from lights from behind, so thats not what I want.

And second problem can be visible from the this gif I made for you guys. So when I move or rotate camera, or sprite itself moves, its somewhat flickers. Without light it doesn't happen. How can I solve that? Is it achievable by shaders or I need to use some dirty hacks?

Here is more info for dear sirs to inspect where problem is. Sprite object in inspector:

Sprite shader I found on the internet and slightly edit it (can't remember what exactly)

 Shader "Sprites/3D Environment Sprite" {
  Properties {
      _MainCol ("Main Tint", Color) = (1,1,1,1)
      _MainTex ("Main Texture", 2D) = "white" {}
      _DetailCol ("Detail Tint", Color) = (1,1,1,1)
      _DetailTex ("Detail Texture", 2D) = "white" {}
      _Cutoff ("Alpha cutoff", Range(0,1)) = 0.5
  }
  
  SubShader {
      Tags {"Queue"="AlphaTest" "IgnoreProjector"="True" "RenderType"="TransparentCutout" "PreviewType"="Plane"}
      Cull Off
      LOD 200
 
      CGPROGRAM
      #pragma surface surf SimpleLambert alphatest:_Cutoff addshadow fullforwardshadows
      #pragma target 3.0
 
      sampler2D _MainTex;
      fixed4 _MainCol;
      sampler2D _DetailTex;
      fixed4 _DetailCol;
 
      half4 LightingSimpleLambert (SurfaceOutput s, half3 lightDir, half atten) {
                half4 c;
                c.rgb = s.Albedo * _MainCol.rgb * (atten) * _LightColor0.rgb;
                c.a = s.Alpha;
                return c;
            }
 
      struct Input {
          float2 uv_MainTex;
          float2 uv_DetailTex;
      };
 
      void surf (Input IN, inout SurfaceOutput o) {
          fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _MainCol;
          fixed4 d = tex2D(_DetailTex, IN.uv_DetailTex) * _DetailCol;
          o.Albedo = lerp(c.rgb, d.rgb, d.a);
          o.Alpha = c.a;
      }
      ENDCG
  }
  
  Fallback "Transparent/Cutout/VertexLit"
  }

Any help appreciated. And sorry for my very bad english, I'm described my problem as much as I can :)

UPD: Looks like latest Unity beta 5.6.0 solves the problem with shadow acne thing flickering, but "shadows from the back in front" still here.

UPD2: Just checked status in Unity 2017.2.0b6 and it works! But still have issues when camera rotates. Here's shader that used.