To me, this means the value of the gift should not exceed $25. I take it this way because that is what it means for us at work for the Dirty Santa gift exchange. Because we have supervisors and managers participating, and the maximum value of a gift from a subordinate to a supervisor is capped at $10, if I find a great deal on something on Black Friday and pay $5 for a $10 value gift, that is all I can give in that exchange.
I can only equate a limit in gift giving to my workplace practice becuase we don't do big grab bags or whatever in my family - it is not large enough to justify such a thing.
Here's an idea...take your grandpa to dinner or take dinner over to his house and spend time with him with just your family. Then skip the 50+ party that sounds dreadful! I would be tempted to go out of town for Christmas instead of doing that. They must have a very large house!
I don't know if I am just feeling sad and sentimental today, but the last part of your post made me sad. Is there anyway just you and your Dsis could go with your mom to the party and leave your family behind? Now that my mom has dementia, I spend a huge amount of time with just my mom and dad and not my family. When mom is having a good day, its lots of fun ti sit around and tell stories that we love and nobody else cares about. Maybe if you and your sister could go with mom, it could be your own little family time and you may find you are having a good time not worrying if your family is having a good time.
It may be you are reading your family into hers (which we all do). I don't picture this being Mom spending time with her kids - but mom spending time with her siblings - something that as we age we get to do less often and value more, while the next generation looks awkwardly at their cousins and thinks "there goes Sarah bragging about her high profile job and all her money, yeah, I'd get to talk endlessly about my trip to Paris if I went to law school and married a cardiologist" - "there is Nicole, is that her THIRD husband? I'll need to ask Cathy, I think she said something about not having married this one" "Boy, it doesn't look like Stevie has stopped drinking yet." "Patrick is as handsome as ever, that man doesn't age." "That ***** that Jim married still has no control over those hoodlums of hers." Or worse, they say it aloud. And the third generation simply thinks "His mom let HIM bring an iPad, I don't know any of these people, why am I here."
It's probably too late OP for this year. However, what my sister and sisters-in-law, nieces and nephews decided early last year (like late Sept), was that each parent bring a small gift for their own kids (under the age of 10).
For the rest of the adults, we did a cookie and recipe exchange. I provided themed holiday trays and a recipe box for each family. My sister and sister-in-law brought moms' and grandmothers' collection of recipes and we laughed as well as cried our way through them. It was so low keyed but loved the focus on the family and remembrance of simpler times.