Your mom should be doing what YOU want, not the other way around! It is hard at such a young age to set a loose nap schedule but it's never too late. My LO stays with a family member a few days a week, my mom one day and me the rest of the week and we ALL have a different schedule for him. Getting in sync isn't always easy when your baby goes various places.
Try reading sleep cues and be consistent in what you do. That seems to be key.