If you are in Glasgow, Scotland there are 2 kinds of very high fibre “pellets” available, Vetcare Plus Digestive Health Formula and Fibafirst sticks. The pellets are long sticks but can of course be broken into smaller pieces. You might have tried them already of course. I have both kinds for my bunny who is a lousy hay eater. The Fibafirst sticks are somewhat lower in fibre (30% vs 32% for the Vet care Plus) but they seem a lot yummier, so if your bun has difficulty eating enough food, I think I’d go for those.

My bun eats fresh grass eagerly. If your buns are vaccinated, you could try foraging fresh grass for them (but again, don’t know if you’ve already tried that).

As for making sure the boy bun gets enough food, the only reliable method I can think of would be to feed him some of his daily food separate from the other bunny. And weigh him weekly so you keep track of his weight.

Wick’s front incisors exist but are generally not very functional because of his malocclusion. The front incisors as you mention are used to help pull in food and rotating it.

I’ve found cutting Wick’s veggies into thin strips, rather than small pieces, is most helpful. Pieces with wide surface areas or that are too short rely on the front incisors too much for rotation and holding.

Have you tried orchard grass specifically? The more leafy Hays. I imagine the crunchier hays can be difficult to maneuver because the individual pieces will not move in the mouth due to their stiffness, but a hay with slight “give” may be more mouth friendly.

Some buns really like readigrass. It’s dried grass, so its softer (and slightly more nutritious than grass hay), but it’s still grass and that’s what the bunny tummy and teeth need. I think Wick makes an excellent point about the crunchier hays, the stiff pieces rather of have to be more difficult to handle if you don’t have incisors.

I think the best thing for Roli would be Critical Care (Oxbow). There are recovery formulas by other companies as well, but I’ve never tried those (where I live, CC is the only option). It’s recommended for recuperating buns or buns that can’t keep weight on. The apple/banana flavor is more popular among buns than the original flavor, and if you mix it up with some (unsweetened) baby fruit purée, he might eat it from a plate or a spoon. It has lots of fiber and all the nutrients a bun needs. That would cover his nutritional needs + give him fiber.