add alpha variables to a customised diffuse detail shader

I have modified the diffuse detail shader so that it now had more layers that are overlaid. I want each of these layers to fade in gradually using alpha. How do I change the shader to allow each layer to have its own alpha variable? Below is my shader code. Thanks for any help.

Shader "Custom/Dirt" {

Properties {

 _Color ("Main Color", Color) = (1,1,1,1)
 _MainTex ("Base (RGB)", 2D) = "white" {}
 _Detail ("Detail (RGB)", 2D) = "gray" {}
 _Detail2 ("Detail2 (RGB) Trans (A)", 2D) = "gray" {}
 _Detail3 ("Detail3 (RGB) Trans (A)", 2D) = "gray" {}

}

SubShader {

 Tags { "RenderType"="Opaque" }
 LOD 250

CGPROGRAM #pragma surface surf Lambert

sampler2D _MainTex;

sampler2D _Detail;

sampler2D _Detail2;

sampler2D _Detail3;

fixed4 _Color;

struct Input {

 float2 uv_MainTex;
 
 float2 uv_Detail;
 
 float2 uv_Detail2;
 
 float2 uv_Detail3;
 
 float2 trans_Detail3;
 

};

void surf (Input IN, inout SurfaceOutput o) {

 fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
 
 c.rgb *= tex2D(_Detail,IN.uv_Detail).rgb*2;
 
 c.rgb *= tex2D(_Detail2,IN.uv_Detail2).rgb*2;
 
 c.rgb *= tex2D(_Detail3,IN.uv_Detail3).rgb*2;
 
 o.Albedo = c.rgb;
 o.Alpha = c.a;

} ENDCG }

Fallback "Diffuse Detail" }