Your buns sound exactly like mine: Leo is the the “Eeyore” slow eater digger type just like Romeo and Arduina is the princess diva food devourer like Bella.
What I had to do was feed them less pellets so Leo would eat right away. I give them 1/4C between the two of them, you can also split up the pellets and feed them several times a day. Starting out you can sneak Romeo pellets at other times of the day. Another thing that might slow down Bella is using those kitty treat balls to put the pellets inside (they roll it around and pellets fall out the holes). As far as veggies, also give them less or several times a day. Make sure that when you put the food down, Romeo comes over to munch. Romeo will have to adjust to Bella’s eating habits (Leo did for the most part). I knew food would be an issue, so during their bonding sessions I would feed them, and then left overs I would give to Leo, to get them use to eating together and add the feeding schedule.
Bella will have to get use to being in the cage. Arduina was the same way, free range 24/7 and ruler of the house. During the bonding I would switch their cages (Arduina was in a cage/pen through the whole process). She eventually got use to it.
Arduina still eats twice as fast as Leo, but I try to make sure eats something and do give him extra treats now and then. He is more on her feeding schedule now, as in he knows that if he doesn’t eat right away, he doesn’t get anything.
Good luck and keep us updated.