Keep in mind I'm not familiar with horses please. So if I'm way off, sorry.
The latest developments, while frustrating, do not cause me concern over Max's overall health. I'm also not surprised by this delay.
There are only 2 reasons I can see to have started and to keep continuing the Max tug-of-war by the uncle. Neither involves anything but good treatment for Max. Either he's so emotionally attached to Max he can't bear to let him go, least likely to me but who knows, or there's perceived decent money somewhere ongoing or future that a "clear title" to Max will maximize profits. I'm placing my bet on the latter. Both options IMO lend themselves to good care for Max. Maybe the uncle has him leased out or is making stud fees off him. Whatever though, I see it as perceived continuing revenue.
I don't think Max is dead or was sold because it would have been extremely easy to be totally off the hook from day 1. "Hey, we really tried. I brought a vet in who did all he could, but Max didn't make it." Uncle is out of the pic and off the hook. "Times are tough and with the vet bills and all, we just couldn't keep him. Someone called about the free horse flyer we had at the feed store right away and came to get him. Sorry, it was so long ago and we don't remember their name and never had their contact info." There are just so many ways for him to have been out from the beginning with any and all issues staying with the nephew.
He may be a complete waste of a person, but I don't see him putting up such a fight just to be an...well, you know. I'm thinking there's just gotta be some money in it for him somewhere. Enough money to justify the lawyers expense and potential legal risk (yes I know that's not much with his buds, but still there's some.) Like I said, I don't know a thing about horses, but I'm thinking to get enough money to make the hassle seem worth it, Max has to be kept in reasonably decent shape. How much is normally paid to lease a horse every month and how long is a normal lease?