What is the ruling on sitting with non-mahrams at dinners and eid gatherings, and can this be progressive, for extended family to adjust as it's new. My family complains I'm being selfish for excusing myself from it as they feel pressured to cover my absence, and can't all of them avoid these events

Sitting with non-mahrams is not allowed, and Shaykh Ibn Baz raḥimahullāh called this custom a bad one that must be left, with the women seated apart from the men. This is not cutting ties: keep them with visits, calls and messages where nothing forbidden is present, and advise your family gently, for even reducing the evil is a great good.