I think Mike eventually sold the milk-round to someone who was going to keep Jazzer on, but that seems to have got forgotten about. Or at least, we haven't heard Jim or Alistair complaining about Jazzer getting up at an ungodly hour and waking them up.
Will found out about George being taught how to poach the pheasants Will is employed to look after, and raised a hefty row about it (justified, in my opinion) so I'd be surprised if Clarrie didn't hear about it.
The thing is, Will is awful in all sorts of ways, but his family treat him so badly that it's hard not to feel that it isn't surprising if he's a git. They were vile to him when he started to work for George Barford. And things like Clarrie telling him shortly after Emma left him that Ed and Emma and George were the family now and he just had to accept it would be enough to make anyone bad-tempered, even if for instance they hadn't used "you'll upset your mum if you don't do it" to make him be Ed's best man when Ed married Emma -- that was just a horrible thing to do to anyone.
And yes, I feel sorry for Mia because Will shouted at her, but at the beginning of the episode she was being the worst sort of sulky teenager at him, refusing to speak to him -- and why? Because she'd blown up about doing too much work, so he'd spent a whole week trying to make sure she didn't have to and then she sulked about that! And he was trying to do something nice for her when he was suggesting the holiday, and she threw it back in his face and made it clear that she didn't want to spend any time with him.
He can't win, he can't break even, and because he has children to worry about he can't get out of the game by simply packing in his job, selling his house in The Green, washing his hands of the whole boiling of them and moving away to work somewhere else where the rest of his beastly family are not around to bully him.
Sorry; rant over, but I do feel sorry for anyone in the position Will has been in since he was about fifteen.