Are adult children responsible for planning and throwing their parents' anniversary parties?

For example, yesterday was my fiancé's parents' 40th wedding anniversary and we did nothing because we didn't know. Last night in a group text his parents started guilt tripping my fiancé and his brother because they didn't do anything for them.

Also, my fiancé and I suffered a miscarriage this year and are newly pregnant again (parents don't know bc we're that early) and we're in the middle of moving. His brother was just in a tremendously ugly custody battle for his 2 year old (which he very recently won). And their parents still expected something from us.