Underweight and overweight rabbits

I normally feed Archie and Izzy in the morning and the evening, but when I held Izzy last week she felt very thin, and I could feel her spine quite easily. I picked Archie up and he is a lot heavier than he was before. I've watched them and Izzy eats her food a lot more slowly, she likes to eat a bit and then come back to it later, but Archie eats his food really quickly, and he'll then try and eat Izzy's. I've tried feeding them seperately but because Izzy eats really slowly I have to seperate them for a couple of hours and on days when I go to college I don't have the time to do that. I've been leaving them seperate for about half an hour to eat some, and then when Izzy won't eat anymore I put them back together and then every now and then I give Izzy some pellets from my hand. I work out the amount she should have per day and I make sure she gets most of that every day, but she doesn't eat all of it.
What can I do to help Izzy gain weight and Archie lose weight?

I can imagine this would be quite a common problem for those who have more than one bun.

Unfortunately I don't have any suggestions, but hopefully someone will be able to help

Have you had her teeth checked? It's just that slow eating & weight loss can be a sign of dental pain.

No I haven't, I didn't realize slow eating was a sign of teeth problems, I thought she would have stopped eating altogether. The rescue checked her before she left the rescue 2 weeks ago and said she was fine, I am going to get her to the vets too. I am trying to make her gain weight by giving her more pellets, and she seems to eat more out of my hand than from the bowl, so I've been giving her extra pellets when Archie isn't looking I weighed her tonight and she's 1.9kg, which I thought was a bit small because she's a dwarf lop x lionhead, and Archie's a dwarf lop and weighed 3.9kg when the vet checked in August.
Thank you for the help I'll phone the vets

I had the same problem with my pair. Gloria was a complete gorb. What I used to do was lock Wolfie in for a little longer so he got the chance to get his breakfast without her pinching it.

Normally rabbits show signs of dental problems before they stop eating altogether, it's just that they can be missed by us. It may be nothing but it is always worth checking as nipping it in the bud now is far better than waiting until she actually stops eating, especially as being underweight increases aneasthetic risks.

I took Izzy to the vets and the vet said that Izzy has small spurs on her back teeth. She said they are too small to remove at the moment because removing them now could damage her teeth, so she's going back to the vets on 16th November so the vet can check her weight and her teeth again.

Izzy is also now insured, which includes her teeth problems so hopefully it won't be too expensive. Izzy is seperated from Archie to eat, but because she eats so slowly they are normally seperated for a few hours each day, and she has some oats mixed in with her pellets to help her gain weight.

Alicia are you sure it covers teeth probs? My pair were with pet plan and are now with PAH and Bruce is a dental bun, but his dentals are not covered by the insurance. They class teeth burring as rountine dental work. Bruce's dental bill is usually around the £70 mark and so never really gets above the excess anyway.