"Would a Casita be big enough for 2 people".... like has been said, a "Casita" is designed for gathering, or for utilities, cooking, a place that gives a bit more room than the confines of an RV....such as a large den for TV viewing with friends, with large comfortable chairs, perhaps as a sewing/quilting room, a hobby area, a laundry/cooking area, or a combination of all.
The majority of RV lots in the Yuma Foothills area...have been developed with 4 distinct RV hookups (tho' only 2 are allowed to be used at any given time) along the outer edges of the property. The lots are in the 65'x120' or larger range. So, 2 RV's could use the lot, or 1 RV and 1 Park Model/mobile home, or 1 RV and 1 house, and in all circumstances, a central Casita could be utilized. If you are looking for room for guests that you cannot accommodate in your RV, you could place a Park Model or single wide mobile home on the lot.
Come to Yuma in the winter, see if it suits you.
Regards
Gemstone