We have an indoor rabbit and he is honestly the best pet we could have wished for. HOWEVER, this is two years down the line and it's taken a lot of learning and chewed wires/furniture to get to this point!
Outdoor rabbits require a large amount of space. Most hutches sold at pet shops are inadequate in size. Rabbits need the ability to be able to stretch up on their hind legs and not have their ears touch the top of the hutch at a minimum. If you choose to keep them in a hutch, they will need daily supervised exercise in a very large run (enough to zoom and binky). Both the run and the hutch need to be properly fox proofed - some foxes can get through the mesh on hutches. Don't forget they'll also need feeding/cleaning out on miserable wet and cold days too so factor in whether you'd be happy to go out in the pouring rain or snow to do this!
Rabbits require a diet of mostly hay, accompanied by high quality pellets (not rabbit muesli!!), with some fresh green vegetables. They graze over the day to help wear their teeth down and keep their digestive tract moving. As a pp said, they can decline very quickly if they stop eating/going to toilet, and as a prey species they will hide any symptoms they have so you have to be extra vigilant (I have spent a few nights syringe feeding critical care food my rabbit at 2am to ensure his digestive tract doesn't stop!)
Both of these rabbits will need spaying/neutering. Please ensure this is done even if same sex pairing. Uterine cancer is common in does that are not spayed, and bucks will tend to be calmer and not spray as much urine for territory marking when neutered. In our experience, we were only able to get ours neutered at 4 months old. He was too small prior to this. Rabbits also require regular vaccinations against myxomatosis/RHD1&2.
Again, as pp have said, not all rabbits get along. They need to be 'bonded' and it is not the case that this will automatically happen if they have come from the same litter. It's like humans, some rabbits will just not get on together. Bonding can be especially difficult with same sex pairs, but also with male/female pairs too.
Our rabbit is happy to be stroked (especially nose rubs), however is not cuddly in the slightest and fights against being picked up. So you may find your child loses interest quickly as they're not like other animals that will sit and be 'loved'.
As others have mentioned, they can live up to 10 years with correct care. You need to work out if this is the type of commitment you want to take on. You also need to think about care if you go on holiday - animal boarding is not cheap!
Please don't assume they will be easy to take care of. I definitely would not recommend rabbits as a first time pet for a small child. I was 29 when we got ours and it was still difficult! But now that we've got to grips with it all we wouldn't be without him.
I think your exH has put you in quite a difficult position and I would recommend that if you're not in the right position to be able to house and care for these rabbits, that you look up local rescue centres and pass those details onto your exH!
Good luck with whatever you decide!