Yummygran1, I think you have me confused with morethan2, who is the OP of this thread. I did say that one of my DDs has occasionally voiced concern that I'm favoring the other one, but morethan2 is the poster w/ the difficult DIL. Thank you for your kind words, anyhow.
I'm sorry to hear about how your younger son and DIL reacted to your recent vacation. I hope you pointed out that you weren't the host and it wasn't your place to invite any additional guests. Unfortunately, it seems as if this may be just another episode in an ongoing history of rivalry between your two sons though, I realize, you seem to think this one is due to YDIL (younger DIL). Either way, I'm sorry you got caught in the middle of it - and through no fault of your own!
Dynasty, if only all adult siblings and their spouses could look at things the way you and yours do!
Midwifecf, I think you've expressed something many older parents often/sometimes feel. But in most cases, IMO, it's not our fault. It's our adults sons/daughters (and sometimes their spouses) who often are the ones getting it wrong. They need to realize the difference between responding to a need and favoritism. And, in many cases, to be glad if they're the one who is less needy (for financial help or otherwise). Sure, there are some parents who really do favor one child above the others. But no one, IMO, should just paint all parents w/ that same brush.