Is it permissible to give the 200,0 Syrian Pounds, recommended by the grandfather and grandmother for the poor and needy, or a portion of it, to one of the female heirs (the divorced maternal aunt) who will become homeless and whose share of the inheritance is not enough for her to buy a house?

As long as your aunt fits the description of those whom your grandfather intends to give charity to, there is no objection to giving her some or all of the money. In fact, she might be more deserving of it, because charity given to a relative is both charity and maintaining kinship ties. This is supported by the hadith of Yazid bin Al-Akhnas, where the Prophet, peace and blessings be upon him, said to him: "You will have what you intended, O Yazid, and you will have what you took, O Ma'n." The point of evidence here is that Yazid generally described those deserving of charity, and Ma'n was among those who fit that description. So, if your grandfather generally described the poor and needy, then your aunt falls under that category. This applies if the will is general. However, if he specified it for an heir, it is not valid unless approved by the adult and sound-minded heirs.