Maxis fibre wasn't around that time when I first install unifi in my area. I asked the person in my neighborhood how he managed to get 2 cables from pole into his house, he told me he had maxis first then unifi. On the phone when I call 100, the cs told me I have to call the last ISP that install their service on tm btu. Basically is like tumpang to stay in people house but you can't ask the owner to move away and you stay in their house. 
He then tell me to call maxis and I get a rude answer from a lady saying I can't split up no matter what, even after terminating and reinstall. But I did ask maxis cs via phone if there is extra port in my area(and yes, there is some ports available) before asking a btu split up because if you ask them for split up then for ports availability they will always come up a reason to say "port is full" because they can't answer your first question.
I could, but it be nice to have separate btu because it's much cleaner. Currently tm have drilled my aluminium window frame just to pull the fiber cable in. The area I planned to place the btu is not too deep inside the house, just drill hole and place the btu like 2 metres next to the hole on either of the floors in my house.