Neverwinter Nights has coop. It even has a dungeon master mode where one controls the game for the other players.
BG3 might also not be suitable for kids anyways. It’s full of gruesome imagery. Like at the beginning you can pull a brain out of a more or less living person. And later on it gets much worse with mutilated bodies everywhere.
Another game to play would be Diablo 2. Also gruesome imagery but more removed from the players. If your machines can’t handle Diablo 2 Resurrected, they should at least be able to run the original. And for the original you would also only need one copy between all players. But keep in mind that D2 is more action oriented.