My team has tried literally everything in sourcetree but we failed. Can someone please tell us what they use to collab in Unity.?Unity collab is an option but we are 4 people so we exceed the limit.

If you have unity student or Pro, u san use the unity collab. You could just create a github repository and make a branch for each of the participants also, it's not the same thing but it helps to organize and let's you update your co-workers codes. That's all I got, hope it helped