We've been to all of the places you're considering: Chef Mickey's, Tusker House, Ohana and Crystal Palace. (We have three boys, ages pre-school to pre-teen and have been taking them to Disney since our oldest was a year old - so we've done lots of character meals!) I'd definitely recommend keeping Tusker House - we love it! I'm not a fan of Chef Mickey's (although we did try it multiple times) so I'd skip that one.
As for a replacement ADR, while Crystal Palace is fine, I don't think it's that great if your kids don't recognize and love the Pooh characters. Our two older boys never liked Pooh much but our youngest likes those characters. The fun of Crystal Palace is watching him recognize and interact with them. Last trip, we just did that at AK instead and made our breakfast ADRs for Tusker House and Ohana.
I'd definitely recommend Ohana for breakfast. We had 7:30am ADRs there in January and again earlier this month. We were seated immediately both times and easily made it to MK before the 8:50am opening show. Even if your kids don't know Lilo and Stitch, Mickey and Pluto are great. I like the food - the juice, pineapple bread, fresh fruit, Mickey waffles and (I'm alone on this one) the bacon are all favorite - they also serve biscuits, eggs, sausage, potatoes, etc. It's a MUCH more relaxing character meal than CP or CM with the food served family style (not buffet) and overlooking the lagoon with the castle in the distance. We stayed at the Poly in January so that was easy, but it was also easy earlier this month to catch a cab from BC.
Happy Planning!
