Is a gift stipulated on lifelong possession and inheritance of jewelry considered a family waqf (endowment), and is it permissible to sell it out of necessity, and what is the ruling on lying to the donor, and is it permissible to borrow with interest to buy similar jewelry to please her?

The condition set by your grandmother, preventing you from disposing of the gift, is void because it contradicts the essence of a gift contract, which entails the donee's freedom to dispose of the gifted item. Books of Fiqh (Islamic jurisprudence) have stipulated the invalidity of a condition imposed by the giver on the donee, prohibiting them from selling, gifting, or utilizing the gifted item, because the essence of ownership is absolute disposal. However, you should not inform your grandmother of what you have done, and you may resort to using allusions (Ma'areedh).