May 2016 trip to the SW

I'm thinking about a trip to Disneyland in the middle of May. We thought we'd go there for a few days then maybe travel up through Bryce, arches, etc and back home. I'm planning on two weeks, but also considered stretching it to 3 and going to NM for a while.

We will be leaving out of Portland, Oregon. We have 3 daughters, 15, 10, and 7 at the time we will be going.

So, any recommendations for this general area. Last time we were at arches was 2008.

We will be traveling with a 40' fifth wheel.