I am in the year of aveilut for a parent. My mother-in-law does not understand many of the halachot of aveilut. She comes to us all the time but we also sometimes go to see her on Sundays and this is very meaningful to her. When we go, we bring our own food and bring enough so that she can join us. She also often has friends come by and we bring enough for them too. We could just go and have snacks she would probably be disappointed and it would be less enjoyable for her. Can we have a meal at her house that includes her and even possibly friends of hers?
Yes in your instance it is permitted. Although normally a person during the year of aveilus for a parent does not attend social gatherings and parties, you situation is different, because you are the one bringing the food, and it is for your family. The fact that others who happen to be there are also joining doesn’t forbid your partaking in your own meal.