Sims dying whilst I'm away?

So I had a large family in one house and decided to create a new household. When I came back to the original household one girl had given birth to triplets and 2 sims had disappeared. I'm assuming they've died but I can't find an urn or a grave so how do I find out what happened to them??

I think when you're absent from the game and people in your family disappear you're just meant to assume that they've died, it's very much a new natural progression thing in the game. It is annoying though that they don't leave gravestones or urns, I think you have to be actively playing for those to be left behind.

Yes, they've probably moved along into the great after sim world, ahahah. To avoid your sims dying while you play another family, go into game options and turn off aging for played households. You can still age up in the family you're currently playing but also keep your other families from dying in your absence.

Oh! To find out what happened, check your sims genealogy...do you know how to do that? When you're playing normally click on the info panel and then click the head icon (I think that's where and what it is though I haven't played in a couple weeks lol) then you can see the history of your sim and their relatives. If they died, they will show up grey and if you click or hover on that sim you can see how they died.
If they died while you weren't playing though, it's almost ALWAYS just old age.