The only way I see Ten Hag being successful is if he has the (as Frank calls it) bollocks to clear out half the squad.
The problem as everybody can see are the players so there's no chance in hell he can come in and try to change the culture or the dressing room without blowing it all up.
From his comments so far, he sounds like a bit of an authoritarian which you do need for some discipline but only if the players buy in, and I doubt this lot will do it.
I'd just do a straight clean up, and get rid of everyone over 25, maybe keep Varane, Fernandes, De Gea, and anyone who comes in has to be asssessed whether they'd fit into the club culturally. You gotta go after street fighters like Rooney who leave it all on the pitch. Saint Maximim from Newcastle would actually be a good fit for them. Kulusevski looks like a steal for spurs, and I doubt they'd sell him on so quick.