Lost Documents - Mother title from city hall and absolute deed of sale

I'd like to ask what can be done in order to produce the mother title of a land property when several important documents are missing?

A relative of mine has a plot of land that was purchased by their father. The family was unaware of the purchase until before their father's death. They also found out that the property in question is not under their father's name but instead it is under their aunt's, who processed the paperwork years ago. Their father was working overseas and entrusted the purchase to their aunt, assuming that it was under the father's name.

Just before their father died, the property was under processing for a sale/transfer under my relative's name. However, in the middle of the process, the documents needed to complete the absolute deed of sale and everything else was stolen from the attorney processing the papers which was done by their aunt. The said documents are the mother title from the land assessor's office, and the deed of absolute sale from a third party where their father had purchased the land initially and a few others that I cannot remember.

My relative's family have been unable to complete and get the proper documentation or I think the absolute deed of sale with their name. However, when they visited the land assessor's office just a few months ago, it already shows that it's registered under their name providing them some proof that the process was undergoing at the time. They cannot sell the property or have no legal documentation that shows it's theirs because the original documents from the city hall is missing, which was taken out by the attorney in charge of the transfer and that was eventually stolen.

They also had completed an adverse claim a few years ago. It was even published in a local newspaper. I've been researching online about how the process goes, they have certified copies of other documents which they were able to somehow recover, but not the mother title and the absolute deed of sale from the third party owner.

The reason I ask this is because their aunt is negotiating with them to buy the land instead. They created a contract stating that my relative's family will disregard their adverse claim to the property instead of a legally purchasing the property and the money will just be transferred to them.

Also I think it might be important to note that their aunt had also falsified some documents proving that their aunt owns the property instead of my relative's family. The third party who initially owned the land is also deceased and no surviving family members can be found as they have tried looking for them.

What would be the best course of action to take also? How can we leverage the adverse claim in this case?

Thank you in advance for your help.

the aunt already sold the property to a third party?

Thank you for your reply.

No, their aunt hasn't sold the property yet. But my relative's family is planning to sell it to their aunt just to legally own the property.

The reason i'm asking this is because I think it unfair that the aunt is purchasing the land for an amount that the land could actually costs. It's a 4 hectare land in Zamboanga City and about 15-20 mins away from the city center.

One of the reasons the aunt also wants to purchase it from them is because there's news about a highway that's to be built within the bounds of their property. So I believe my relative's aunt is planning to purchase the land, benefit from the goverment payment for the right of way for the roads to be built and then resell the house.