I have this same thing going on in my family. There are five kids in my family, one lives in Oz, the rest here. One brother is married to a... trying to be charitable here... well, she's irksome.
I wasn't there for the blowout over how and/or who would get presents, or maybe it was over the price, I dunno, but it ended in two brothers trading blows and 6 or so years later, the only people it really hurts is the rest of us. We have to plan two christmas, two easter, two thanksgiving, several birthday parties and other events, all so the selfish parties don't have to be in the same room with each other.
So, as one of the people who've had to suck it up, put up with the bullshit this rift has caused, I say grow up!
Your kids deserve to know their family. You, grandparents, the drunk uncle, the emo niece, the crazy great aunt, who. ever.
Your kids don't deserve the gossip, the pettiness, the bickering, the general histrionics. You have a feud happening, they have nothing to do with it.
Let them live their life and if you don't freak out, they will share stuff with you. They probably think you need the buffer of the lie, not the other way around. Prove to them you don't.