We've done Universal and Disney in the same trip and I would recommend a split stay.
Universal hotels will accommodate 5 and you get the advantage of the unlimited express pass. One night will give you two days of the pass.
I also recommend doing the Universal portion of your trip last. If you do it first (like we did), then you will listen to your children complain about the lines at Disney (which really weren't that bad as we went during a slower time of year) and asking "when can we go back to Universal." My children, who are thrill ride junkies, also declared the Disney rides "lame" after Universal. Admittedly, we had been to Disney a number of times and that was the first Universal trip (but definitely not the last) so to them everything at Disney was a "been there done that" while everything at Universal was new to them.