Oh your father is dead allready.
Yes odd a lawyer didn't solve the documents before start building. But perhaps he thought it would be no problem, because it's family.
But if it's no problem with them, who are owners now (as you aunt) then try to solve it now BEFORE the unfaor cousins get any right to demand anything.
Couldn't buy out the others because of
they didn't want to
or because didn't have money? But he did spend money at the house...
"can i ask what provision in the law that states that "property(building) vs land in terms of value, which is higher""
It depend of location and building. Sometimes the land is more worth, sometimes the building.
But that's irrelevant when owners are same to all.
(In theory owner of land and owner of building on it can be different (=building on leased land)
BUT then the building CAN'T be used as collateral if wanting to borrow, so in many cases that's a BAD solution.)
By the documents aren't in order, you will have to make all the other owners agree to a solution to get it solved somehow.
One more solution idea:
Asuming the land is TITLED, you can use the property as collateral to get a loan to buy out the others.
With property as collateral are interests much lower than what's common for other loans in the Philippines. Around 10 percent per YEAR. But count proper before doing this so you can pay in time, so you don't risk losing it by Foreclosure.
Then your cousins can pay you RENT for the 4th floor
to assist you paying the loan.