I would say this is a pretty one off and unusual situation.
You have to go to see an unwell relative.
Your sisters have to go the exact same time (presumably as it’s the Bank Hol, so better to travel for longer)
Your parents’ house has had an unusual change of layout meaning it has a double room for your parents and three box rooms. You are aghast that people struggled with this, but you didn’t explain it to begin with, and it is unusual.
You can’t afford a hotel.
You can’t drive yourself.
It’s too far for him to drive you and drop you off.
You have fainted, so can’t travel on the train.
Your DH sleeping in the sofa or the pair of you sleeping together in the lounge room on a double airbed/mattress is the best bet, especially as you are bringing your dogs which will need to be let out into the garden. By you/DH.
As you’re having twins, your plans for staying there will have to change anyway.
Whinging about him needing privacy means you are ruling out about the only possible solution, other than forcing your sisters to give up their beds. It feels like you are creating a situation here.
If your sister slept on the sofa, your husband would have to wake her up and invade her privacy when he’s letting his dogs out anyway, so it makes sense for him to be on the sofa, dogs in with him and he’s up early to sort the dogs and dressed by the time everyone else is awake.