My spouse and I have a Get. Can we eat a meal, shabbos or yon tov, together (at her parents house) with the kids. I have been told we are not supposed eat a meal together or to be in the same house together.
That is correct, you and your ex spouse should not be eating a meal together or talking to each other if it isn’t absolutely necessary. The communication that is inevitable, such as things related to the custody of the children etc. is not recommended, but if it can’t be helped we can be lenient, however eating a festive meal together in a family type setting should not be done.
E:H 119-8,9, Aruch Hashulchan ibid 30.