Mom beginning to favor my sibling. How do we handle this?

It's the Mother-Son relationship:) Like Daddy's and little girls. Let him explain to her that he needs your help. He needs to be firm about it. Just let him have that power and you help him with tasks as you both agree.
How nice that you can work together. Blessings to you both. And Mom:))) xo

I would agree, it is your brother who needs to firmly draw the line and tell your mom that there are times he can't be there but you will help and she will still be safe.

Agreed, part of your collaboration is to collaborate on dealing with this too. Also, she doesn't get to have everything her way all the time any more than a child does -- you and I don't get to have everything our way all the time either, do we? Pay attention to what your goal is here: You and your brother are collaborating on actions that are in the best interests of the whole trio, so that you can sustain what you are doing as needed.... NOT the goal of pleasing your mom in every little detail. If you adopt that second goal, even unconsciously, you're screwed over the long run. As things get harder you will discover that you have trained your mom to be impossible....

Haven't you ever heard about mothers and sons, dads and daughters? There is a stronger bond between the opposite sexes and I'll bet it has nothing to do with your brother. My mother thought her son (my brother) was her husband. They both had the same name and mother believed her husband was taking care of her. When he moved back to CA, others took over and it did not matter. Things will go downhill in the future, so stop thinking this is about you. It is not! Dementia persons have their own thought processes and do not try and understand it. Just get her the meds by either one of you, and you do not have to EXPLAIN. She will forget later anyway. She does not have all her thinking capability and you have to forget how she was in the past. This is present condition and you have to adjust! Best wishes.

So true, your brother has to set the boundaries. She will listen to him before she will listen to you. Right now I am the favored sibling because I am the caregiver. I am the one who has to set boundaries because otherwise her neediness will empty me and I will not be any good to anyone. Loving firmness with boundary setting. Hugs to you.

Do not take this situation personally. As noted by the other respondents, it's part of the mother-son syndrome. My mother sometimes will listen to me. However, when she becomes stubborn I have painfully learned to go get my husband or brother to ask her to do what needs to be done. It's hilarious! When my husband asks her to do something she dutifully does it. I used to argue, coax, pull my hair out when trying to get her to just change her depends. Now I ask 1 or 2x. If she resists, I walk away and come back with a "male" in tow and ask him to ask her and she goes and does what he's asked her to do. Have your brother explain to your mom that he needs "your" help. And she'll probably take it from there. It's not you, it's her brain that's confussing her.

He's her baby boy. I took care of my Mom full-time, but whenever my brothers came over to do anything for her it was like Jesus himself came down from Heaven and gave her a hug.

My suggestion: Have your brother gently tell her that the arrangement between siblings works for him. Have him ask her for help in allowing the medication task to be shared between the two of you.

If it were me, I'd add a special moment to my time with Mom. Give her a massage, manicure/pedicure, or just lotion up her hands doing a hand massage. Make the time you spend with her special and not so clinical. Sometimes it is OK to baby our elderly. When she's gone, you'll wish you had made every moment count. Every good memory is a gift.