Will being at the meeting was a good idea of for no other reason than Zach had a safe ride home after, rather than trying to drive a hot little car while thoroughly upset.
Seriously, just his being there and dealing with Wally's animosity head on shows that he does really care for Zach. There are not a lot of 16/17 year old guys who would put up with that sort of nonsense and not walk away. It's important for Zach to see that caring other places than the bedroom at this point.
I can also see that the fact Zach lives with Frank and Isadore may be another point of contention with Wally. I can see the councilor wanting to at least talk to them on the phone, if not have them come out for a sit down with Wally and Clara. I can easily see Wally blaming Frank for "replacing" him in Zach's life.
And then there is the whole power play thing about how Zach will support himself should Wally and Clara disown him. Do they really think Brad would leave them in charge of the trust money should they do that, rather than set Zach up with an allowance and replacing them as trustees? He has done it once already with Gathan, when it became obvious he would not be fair.