Thanks everyone. We're definitely getting closer.
We are about to book our vans. We've spoken to Apollo and can get a 30ft wanderer for the family of 5 and something a little smaller for the family of 4 (that said they would be happy with a wanderer too - apollo seems to only have 1 available for our dates 20 May - 3 June.
We may have left our run a little too late. Just wondering if there are some other good companies anyone would suggest that we can try.
I checked as well, Apollo don't allow travel through Death Valley. Thanks for letting me know.
So now we'll leave Vegas and head straight to Yosemite, with a stop on the way. Thanks for the link to past opening dates of the Tioga Pass. We'll definitely have to wait closer to the time to see which way we'll have to go. In the meantime I'm just working on 2 routes.