I was in a situation where I was “ forgotten “ on some meaningful occasions.
What I would want to know is why ? You say they are adults ? What kind of adult just does what they did on the orders of their mother ? Wow , don’t they have their own minds ? I would reach out to them and try and find out why they ignored your birthday. Do they communicate with you otherwise ? My main beef would be with their mother, who you had some words with. Have some more words with her and straighten this out , one way or another. That’s what I hate about things like Facebook , it’s so hollow. Remember the days when people actually sent out birthday cards ! Social communication is really no communication. Get on the phone! Find out a what the heck is really going on.