Don't try to see everything. See about a third in each park, then you can start having fun.
Fast passes can be worth it, but they are a pain to get and plan around. Balance all the planning with actually enjoying your time there.
Live in the moment, not for what you're about to do next.
In other words, it's better to cancel a reservation or junk a plan than to cancel the fun / time you're enjoying with your family at the moment.
In other other words, plan on 8 to 12 hours of just being there.
Character meals are overrated. You only have a couple seconds with the characters. Don't plan too much around seeing characters. Plan more around seeing your family.
If you're gonna commando the parks (and possibly stress everyone out), stay in a cheap resort. Save the money for your next trip when you spend most of the time enjoying the resorts.