Package,
you sound like you don't want to get the df. I can understand with family connections and all. But, the rewards of being out of the elders sphere of influence and investigation is totally rewarding.
If they want to discuss birthdays, I would simply ask them what Bible verses specifically condemn birthdays.
Since there are none, tell them that you are having a difficult time understanding their reasoning, and it has left you very perplexed why they would make such a big deal out of a non-Biblical issue.
If it gets nasty, tell them you thought there had been a change, since the WT Society celebrated the 50th Birthday of the United Nations.
Best of all good things to you.
Brant