Fence Between Neighbors

I built my house and paid for all my fences 20 years ago. The back and east fence were replaced last year when a neighbor approached me and asked if I would split it if we had double sided or I would pay 1/3rd if I saw the posts. We all went 50 /50.

I brought this up with a neighbor on the final side and he said he is fine with the fence but he will sign off if I want to do it and pay for it.

I am operating via legend or is splitting the cost either 50-50 or 2/3 1/3 standard practice in the Houston area?