Head tilt + blind in one eye makes me think E. Cuniculi. Does the blind eye have a cataract? If so, it’s probably E. Cuniculi. Generally, E. Cuniculi isn’t something a rabbit gets over on it’s own. E.C. can go into a sort of remission during which it isn’t causing additional symptoms, but it almost always comes back. Sorry to say, but if your bunny does have an E. Cuniculi infection, whether it’s in remission or active, it will almost certainly eventually kill him, and it can be a painful way to go.
Make sure he has shade, access to plenty of water, and you may want to supplement him with unflavored pedialyte. Coconut water can work, too, since it has electrolytes, but it also has a fair amount of carbs, which won’t do your bunny’s GI tract any favors if you use it long term.
Ice packs in his favorite spot, rotated out during the day, would help. Greens doused in water, and dense veggie with a high water content like radishes, romaine or cabbage hearts, would help him stay hydrated. (These types of veggies are generally contra-indicated for rabbits. They upset the delicate GI tract if used for long, but they will help him stay hydrated. It’s a very short term solution, though.) Plastic water bottles full of frozen water scattered about would help, too.
All of these things would help more if your bunny were somehow separated from the others, so that he could find and access the pedialyte, ice packs, food, and frozen water bottles easily. If you can manage that, make sure it’s completely shaded, and gets air movement. Shade doesn’t help as much if the bunny is in a very small space that his body will heat up further, or behind a larger building that cuts off the breeze.
In the meantime, can you work on your folks? Explain to them that bunny can live inside with no muss and no fuss if he’s in a cage that’s cleaned regularly? I got my inside cage used for about $15 from a Craiglist ad. I don’t know what your parents worry is, but if you can figure it out, and counter it, bunny would be much happier inside where it’s cool and safe than outside where it’s too hot.
.
