Buying a lot from one of the children whose parents as owner are both dead.

I would like to ask about my plan to buy a lot which is 227sqm. to one of the three children whose parents are the owner but both are already dead. Three of the children are still alive but they're all living in abroad, but one of them will come to philippines again to sell the said lot as he said through his lawyer. The lawyer also told us that the sibling who will be coming will have an SPA saying that his/her two siblings are allowing him/her to sell the said lot. Is it enough that he/she has an SPA to sell the said lot to us? His/her lawyer also sent me a contract to sell and/or deed of assignment, but i was been informed by a friend of mine that an additional extra judicial partition or settlement is also needed before buying the said lot. Please give me an advise regarding the matter. Thank you.

Yes if the 2 sibling already sign the SPA it's ok

You said 3 of the children are still living. How many children do they have? If some of der children are already dead,then der children still have the rights to der grandparents property. So, Yes. Extrajudicial is needed.