That’s so sweet that you can be there for your brother and support him! I have a couple of suggestions that can pay tribute to your mother. I would suggest “A Song for Mama” by Boyz II Men or “Two of Us” by Louis Tomlinson. Both are a little emotional, but I think they could work! If you want to personalize it, maybe you could do an instrumental of one of her favorite songs or even potentially a lullaby she would sing (if there is one). Wishing you all the best OP ☺️