Need advice on land tax issue after selling half of our property (Philippines)

LOCATION: Philippines
Hi everyone, I hope someone here can give me some guidance. I’m from the Philippines.

Here’s what happened:

• We bought a piece of land and have a proper deed of sale for it.

• Later on, we sold half of the land to a buyer. We also have a deed of sale for this transaction.

• We agreed to split the payment for the property taxes (amilyar).

Now, the buyer is pressuring us to pay ₱30,000 this week, saying it’s for the process of separating the tax declaration (to subdivide the tax obligations). He says that if we don’t pay our share now, he will shoulder the full ₱60,000, and even if it goes to court, he will claim the entire property, not just the half he bought.

I’d like to ask:

-Is what he’s saying valid under Philippine law?

-Does he have any right to claim the entire property just because we can’t pay our share immediately, even though we have separate deeds of sale?

-What should we do to protect ourselves legally?