Re: I can't organize birthdays for my twins...

@Enderia7  With packs, do you really mean mods? Or do you mean that you uninstalled all your expansion and game packs and just played the base game?

Your sims, are they vampires, and perhaps teens?

I found two explanations for this searching: mods; and bug, see this bug report:  https://answers.ea.com/t5/Bug-Reports/NEEDS-INPUT-V-Can-t-throw-birthday-party-for-teen-vampires/td-p/7190695

Always click Me Too on the first post if it matches you issue, this is to track how many players are affected. If you post in the thread, please be detailed about your issue, it serves practically no other point otherwise. (But clicking Me Too does 🙂  )

I do not have Vampire pack so cannot test if they indeed are vampires. Hopefully you'll come back with a response though and tell more 🙂