Wow, Lillabelle is a fast eater! That makes sense that he's lost weight if she's been eating his after she's finished her own and he's taking a break after less than half his pellets. Has he always taken a while to eat his pellets, where he stops before he's eaten them all? Just wondering in case it's a new thing and he might have some dental trouble. Hopefully that's all it is, though, that Lillabelle has been eating Mischief's food, because that's easy to fix by staying with them as they eat and making sure they both (only) eat their own food.
Giving them their veggies that way sounds like a good idea, too, if you can keep Lillabelle from eating Mischief's food. Otherwise feeding them separately might work better, but, yes, if you can just let them eat next to each other that would be better since they're still bonding, I agree. It's really understandable that you've been trying to give Mischief not too many pellets and Lillabelle extra, since he was a bit too heavy and she's growing. Accidentally giving a bunny too few pellets in a difficult situation like that is easily done, so please don't be too hard on yourself!
Also, the photos you posted just now and last night are so wonderful.
Mischief has such a fluffy belly! I love the photos of him playing with his ball.
And Lillabelle looks so dainty.
They're so cute, cuddling together.