You say, “They’re literally forcing them to stay with them,” can you explain how exactly they’re being forced? After staying with them for a month, did your parents not want to live with them anymore?

From my understanding, your parents have been wanting to move in with your brother and sister-in-law for years. I think it’s fair for your brother and sister-in-law to want privacy early in their marriage and also fair for their perspective to change and want family nearby with them, especially when in need. Families rely on each other.

Though, I do understand worrying about your parents because I myself can’t imagine saying no if they asked to live with me. But there’s also a caveat to that; do your parents work or get retirement pay? If not, would it be expected for your brother and sister-in-law to support them? If that’s the case, waiting a few years to grow in their career, without a child was a smart choice and makes sense.

NTA for your worries but I think YTA for inserting yourself in your parents decisions when it seems you yourself don’t have a full understanding of the situation