Let's get the gang back together!
0 points (average length 0 bytes, 2 unique language)

I'm assuming we can define acceptance and rejection as the output of two different values.

The gang size is 2 (the languages are 05AB1E and 2sable), and the program is the empty program.

For some reason, both an empty 05AB1E program and an empty 2sable program appear to outputs 2 (plus a newline in the case of 2sable) when the input is not empty (i.e. a different program; rejection). They output nothing if there is no input (i.e. the same program; acceptance).



Since I "can even count the same program multiple times if its a polygot", these are two programs.

(I know neither 05AB1E nor 2sable at all and just tried golfing languages in TIO until I found some that seemed to work, so this answer might be wrong if they output something else for some specific inputs.)