Best way to route waste pipes

[DIYWarrior]

I'm renovating an ensuite bathroom and would love some advice on how best to route the waste pipes. The existing set-up is in the photo attached, where the Green marker is the current shower waste, Red is obviously the WC waste and Blue is the existing basin waste. This room is a 2nd floor side extension to the original house (the original house stack is boxed-in and the main bathroom and kitchen drain into it). I'm guessing whoever did the original plumbing put 2 x 90° elbows on the shower waste to attempt to stop backflow given the WC waste drains from above it (We never really used this shower so can't confirm if there were issues or not with it).

I'd like to move the vanity unit/basin but it'll mean it's waste is below the existing WC pipe. It'll also mean drilling through joists unless I route it along the brick wall the unit it attached to (that wall will be battened out).

What's the best options here in terms of waste routing for the shower and basin waste as my understanding is I want both entering the main stack above the WC waste?

Any advice appreciated!

 

[blup]

I believe there is a minimum gap between pipes going into the main soil pipe, otherwise seems fine