YANBU OP.
As per previous posts, they are coming from Spain not from Australia, so even under normal circumstances a month is a very long time for a visit.
Personally I’d rather have 4 visits for a week than one for a month - if planned flights aren’t prohibitively expensive.
The key thing here is that you really don’t know how you will be after the birth. Even if all is textbook, as a new mum you’ll be tired, trying to establish feeding/routines, wanting to be in comfy clothes, BF’ing on the sofa whilst napping whilst the baby does.
The last thing you will want/need is overnight house guests (even the most helpful) where you feel you have to feed in a bedroom, have responsibilities for being a host, not being able to rest when you can, sharing bathrooms etc etc
It’s understandable they will want to see the baby as soon as possible, but that can’t encompass staying with you in those first few weeks.
Staying at a hotel and visiting for a few hours for - just like your parents is fine. But that is a few hours - it’s not turning up at 9am and staying until 10pm.
If they want a longer visit then they need to wait 3/4 weeks for you and your DH to get used to parenthood. Even then they shouldn’t come for a month - a week at most.
Your DH gets to lay the ground rules here when he’s the one whose gone through labour, has sore leaking breasts and is bleeding, exhausted and emotional due to a hormonal flood.
You really need to stand your ground here. Those first days/weeks are so important and you’ll regret it if you spend them feeling a stranger in your own home who has to tiptoe around house guests.