I am in awkward situation and I feel I can’t give advice.

A few years ago I had three mini rexes. Two were a pair and one single. I had tried bonding them into a trio but it didn’t work, and I didn’t want to try and force a bond that may later fall apart and leave me with three single buns. We then had the idea to try and find the single bun a new home, so that he could find his own partner and live in a pair, as we weren't in a position to take on a fourth rabbit. A family friend offered to take him, and we agreed as we have known them for a very long time, they had owned guinea pigs before and had some knowledge from looking after my buns. He settled in really well and he had a lovely setup. They got him a friend and he was a happy bun. Unfortunately not long after, his partner passed away. I asked whether they were going to get him a new friend but they said he was happier alone. From seeing him in his bond and now, he was much happier as a bonded bunny. They down-graded his setup to a smaller setup, which isn't really suitable and have started feeding him on muesli. He is now an extremely overweight bunny, living alone, and completely antisocial. When you even go to touch him he runs away. I know deep down he is a big softie and he used to love his cuddles. It is just heart breaking. I have tried in the past to tell them about his feed and for them to try and give him more hay, but there is no change. They are moving house so he will hopefully be getting his bigger setup back soon. But any ideas on approaching the subject? It is the parents who look after them and I feel I can’t tell them what to do as they are older than me. My mum has tried telling them too, but nothing has changed.
Thanks

I've been in a similar situation, and unfortunately, the rabbit died before I had a chance to do anything. You could offer to take the rabbit back, on the basis that you could give him a better life than they are currently giving him. OR you go down the route of offering to educate them; explaining that they are sociable and need to be with their own kind, explaining that being overweight puts pressure on their joints / increased risk of arthritis etc etc. You can also explain that if he is happy he will probably be much friendlier and cuddlier (thus making it more worth their while to look after him better). Failing that, the only other thing to do is shop them to the RSPCA :/

Good luck though, I hope they listen!

You could drop in to conversation how helpful this forum is, they might just take a look and be inspired by other peoples set ups so they are tricked into thinking its their decision rather than a critism from you. Or similarly if you get Rabbiting On, ask them if they'd like to have a read of them so they are getting drip fed good advice.