Tub and shower drain and vent

[Bandrusko]

I know I made a mistake and have an s trap. I also made a mistake and have combined the venting below the flood plain. Someone gave me some advice and said to come down the middle and branch out left and right, the only issue is that I have to go out 30” because of cantilever, how to I go backwards?
Please help.

 

[Jeff H Young]

those vents cant connect together and those cant be dryvents either