May I keep the items my mom gave me before she died?

If she owned the items and truly gave them to you for you to have permanently, you are entitled to keep them. A Will only controls what happens to assets owned a second before death, so if she gave the items to you they are yours. The problem will be convincing them, but you have possession so just do not give it up. If they sue, they have to prove it was not a gift, and who do they have who can state of their own knowledge they were present when she gave it to you and said it was not a gift.

Yes.

Certainly. These were completed gifts.