I just made a photo cake for my daughter's 30th (it is posted in my album) You could do something like that with cherished family pictures! And add the flowers that all moms love!
Last year I was wanting to make Mother's day cake for my Mom.I started thinking that I know a lot of mom's who could use a special treat.I made a big sheet cake and cut it up into 4'' pieces.I could try all kinds of different styles and go nuts on them.I even made boxes to fit them. I found 6 cake pans at a yard sale. They are 2''by 6''? So i had to race home and make more. I ended up making 19 little cakes! It was so much fun and everyone loved them! One lady choose to share her cake with her only child.
My advice is make a general sheet cake to fit everyone then do small individual cakes so each mother can take theirs home and celebrate in their own way.