I don't believe that an official opening date for the pier or an official ending date for the fest have been announced, so nothing is for certain.
The pier is supposed to open during Pixar Fest, and I doubt Disney would go through the trouble of changing the whole fireworks/entertainment setup just for part of Summer, so I think it's really likely that Pixar Fest is going to last all Summer.
As for the pier, the only official word is "Summer", but I doubt they would say Summer if they meant the very very end of Summer. I've seen speculation that it will open Memorial Day weekend (the start of Summer), or on a date in June. I think it's really likely that it will be open by July. I have no real information to back this up other than a hunch that they wouldn't say "Summer" if the intended to wait until August. I think you have an excellent chance of catching both if you go in July.
I hope it's a great trip! My cousin did WDW with Make-A-Wish many years ago. His first choice wasn't possible for him medically, but from what I heard Disney was great and really helped him forget he didn't get what he originally wanted.