Issue with grandparents

HI all,
I need some advice on what I can do about my FIL. Bit of back story, My MIL passed away a few years back, before that, my in laws divorced and started seeing new people. The woman my FIL started seeing (still with her now) is a one of a kind pain in the ass. From the day we met, she has made me feel like an incompetent mother. She makes digs at my parenting style, at how I keep my home and when my husband and I used to go on holiday, she would come into my home and clean it while we were away. (My FIL owned the house, we rented it from him).
Anyhow, when my oldest daughter (almost 9 now) was younger, FIL and his GF asked to have her overnight. She is autistic and hadn't ever really spent a night away from us where she wasn't more than 5 minutes away. She'd had an anxiety attack that night and we picked her up. Since then, we've been hesitant to let it happen again.
So November last year, FIL wants to have both kids overnight for the weekend. No dramas at all. Kids were excited so we said, "sure, why not?"
Now my youngest is an extremely picky eater and can be difficult when trying new things, so to make things easier on FIL and his partner, I packed some snacks, fruit, bread and cereal in a bag for my kids so they wouldn't have to shop for them and would only have to worry about dinner. Long story short, I got the bag of food back, untouched when the kids were dropped off and then I was told my the GF, "You're kids don't eat very well do they?"
That obviously caused some issues, as did me finding out that after telling them my youngest doesn't like showers and prefers baths, she was forced to have a shower and cried the whole time.

Fast forward to now. It's been 6 months since the last time they have seen my kids, their choice, not ours. We asked them if they'd like to have the girls overnight, they said sure. My FIL drops them off the next day. We chatted and he suggested maybe he could have my oldest by herself one time. I thought, sure, that'd be good, our kids don't really get to do much with us, without the other sibling, so that'll be fun. I find out this morning that the reason he only wants my oldest is because apparently my youngest is "too much hassle" Are you joking? She's 5. Sure she's a picky eater and she prefers a bath over her shower. But really?

It has angered my husband and myself because I feel like that is totally unfair on my youngest daughter. I would be more than happy for them to have them separately if they wanted to actually spend quality alone time with them but I feel hurt that the real reason is so awful. He's their only grandfather as my Dad passed away when I was younger. Am I being unreasonable? Or am I totally warranted in my reaction? What should we do?