I probably am.

A little backstory:
DH and I live next to my parents, we see each other every day, help each other out etc. DH lost his mom 4 years ago. His dad lives more than a two hour drive away. BIL lives like 5 minutes from FIL.
Sometime I have the feeling that FIL is jealous of my parents, but he's never been really nice to DH since his mom passed, so DH is not keen on going to visit.

Yesterday FIL told us on the phone that BIL is going to Gran Canaria for 3 weeks and if DH would mind coming and doing the grocery shopping for him. (FIL has ALS and difficulties to move, but he has also in-house care that comes by every day) DH was confused and said maybe, depending on work and if LO is ok (LO has chicken pox right now, but who knows what else happens, he's also teething and I'm thankful for some help... and I believe DH wants some extra time with DS)

So today BIL send DH an email telling him that he goes to see FIL everyday and that he will be away for 8 (!!) weeks and that DH should go fee their father every day instead of him. And if he doesn't want to go there that often he should go at least 2-3 time a week to do FILs grocery shopping. DH works + works/writes on his dissertation + has a 6 month old son + has a house in the middle of a renovation + a vegetable garden that I cannot take care of all alone.
I'm really angry that BIL orders DH there without even asking so that he could go on vacation for 8 weeks. And he asks one (!) week in advance... I haven't been on vacation since our honeymoon. We wanted to visit relatives in September, everything's booked. Now we should stay so DH can see FIL? Maybe I'm irrational. Maybe I should be thankful for all the times that DS can still see his grandpa. But I'm just mad. I don't think this is ok. We have plans. We have work to do.
DH is only sad because they didn't really ask – to him it felt more like an order...

What would you do in that situation? I can really use some advice!
Am I wrong for being angry?