let me try this as well as i am only an ordinary person, not an authority of law.
1. do the bank can take our property because of the unpaid loan she made for her bestfriend?
-> it depends. if she made that as a collateral, the bank can take it.
2. is it possible that we will lost our properties and what legal actions do we have to do to avoid lossing it?
-> it's possible. you can go to court and question any legal actions that the bank or anyone will issue upon you.
3.is it legal for them to take the property in the philippines to think that the loan was made in hk?
-> im not sure if international law will apply here but if HK can show that they have jurisdiction over this kind of case, surely they can. but as a general rule, Philippines law should apply here and any transactions made overseas is not binding unless stipulated in the contract.
4.the loan agreement was signed by her in hongkong, is there a law in the phils that can stop them from applying the agreement in the philippine law?
-> article iii, bill of rights, section 1.
Section 1. No person shall be deprived of life, liberty, or property without due process of law, nor shall any person be denied the equal protection of the laws.
5.what is the worst scenario in this case?
-> long litigation.
my best advise is, consult a lawyer of your choice.
also, find a similar case like yours and try to apply it in your case. if there is none, most probably, your case will become part of supreme court decisions later and our jurisprudence.