What about cooking a meal (or several) for them during your stay? Both my mother and my mother-in-law are absolutely tickled when me or my husband cook for them. Depending on your cooking interests, it can introduce them to new dishes they've never had before, and it allows some really great quality time together. It usually means a lot more to people than paying for a dinner out. And everyone has to eat, right? I think it also scratches that itch of 'yes Mom I really am going to be okay - see I can cook a meal for myself and others, so stop worrying!' without directly addressing it.
If your Mom (or Dad, or Grandmothers) also enjoys cooking, then you can also try new recipes together, and maybe bake some treats for the grandmothers to bring over (idk who's under what roof in your family.) And if YOU don't like to cook, then maybe bring some recipes you'd like help with mastering since I'm pretty sure it's every parent's mission out there to make sure their kid is well fed no matter where they live or how old they are.
I think cooking lessons would be especially meaningful from the grandmothers in your life if they have dishes they grew up eating that they would like to share with you. My grandmother in law was polish and my husband and I asked her to show us her blini recipe and it was a lovely experience for everyone. She was still living independently but couldn't really cook for herself anymore and we couldn't believe that NO ONE else had ever asked her to show them! (Yes, they were delicious, and now we have a family recipe to pass on.)
Just some food for thought (ha!)