If my mom is still alive but has Alzheimer’s, can I get a copy of her Will?

If your mother is still alive, the will is irrelevant: a will only takes affect when a person dies, and while they live, they--or people with legal authority from them (like a power of atorney) or over them (like a court-appointed guardian or conservator)--can spend, sell, give away, etc. their money and belongings regardeless of who might get those things under a will. The will doesn't control what happens to assets/items/money/etc. while a person is alive.
The real issue is not the will, but whether 1) do they have the legal authority (e.g. a POA or guardianship) to sell your mother's items, since if they don't, they are stealing from her; and 2) even if they have legal power, are they doing this in her interest or in their own--someone with a POA, for example, can sell items to pay for the medical or other needs of the person who gave them the POA, but not to pocket the money themselves, since they are bound by a "fiduciary duty" (an obligation imposed by law) to act in the best interests of the person giving them the POA.
If you think your family does not have the legal authority to do what they are doing or that they do, but are abusing it, you can contact your state's elder protective services agency or department or possibly the local police to file a complaint, or speak with an elder law attorney about what kinds of legal actions you may be able to bring to protect your mother.