Oddly enough, I have already told my daughter that when or if I have to go into a care facility the first thing, I want her to give me is a doll or the dolls I have already made and have. I know they will give me comfort and security. I have to admit I would also become concerned that your mother has tried to feed them and is concerned that their "mother" hasn't come for them? I am not sure what the answer is for this problem. Perhaps of you offered her an empty baby bottle she might be satisfied? But then there might be a problem of her filling it with milk or water? I don't know what advice to give you. But I can relate to wanting a doll for comfort.

Walmart used to carry those bottles.

I've seen people with dolls at care facilities and it makes them happy. Whatever it takes! They won't let go of them or out of their sight either. It's the mother instinct. there is a doll on the market with a bottle that when it is tilted in the feeding position it appears to empty. You might be able to buy a bottle like that separately too. I will look online for you. Here is one..https://www.amazon.com/Click-Play-Magic-Disappe...(Phone number can only be seen by the question and answer creators)&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4584413735917161&psc=1

Have you seen the Alzheimers baby doll. Ir looks and weighs the same as a baby. Has real hair, smells like a baby and moves its head side to side. I have one I found at Goodwill and bought because it is so real looking. The cashier thought i had laid a real baby on the counter.

My mother had a doll for about 5 months before she died last week. That doll was a life saver. She would talk with her, sing to her, whistle, and, yes, try to feed her. I had to wash the baby doll often, but it was her companion. A few weeks before she passed, she got agitated with me and I tried to calm her with the doll and she said, "that's just a doll! I said"yes, but that's your baby doll and you love her." Then. I quickly changed the subject to distract her. That was the only time she didn't think it was real.
I hope this helps. In her world, the dolls are real.