Issues with grid based building...

I'm making a multiplayer game with a building feature similar to rust or fortnite, and I'm running into two problems

here's the code I use to prevent walls from being on top of each other

This works but causes walls from doing this

This is something I want to happen, and to add insult to injury this happens on the peer's end

So, what I'm asking is for a solution to this either for the grid or the building detection.