Your reasoning seems quite sound to me. You may have to arbitrate some heated discussions between your two DSs as to who gets the cabover bunk, unless they'll agree to split a bed.
I'm not personally a big fan of slides, particularly for older rigs. They seem to me to often be somewhat of a weak spot (structurally, in terms of sealing) and are another thing to break down. A slide obviously doesn't offer any more room while on the road, and it sounds like you'll be spending quite a bit of time (relatively speaking) moving rather than stationary. However, that's more my biases than any absolute rule.
If/when you look at units with slides, do pay some attention to how things are accessible (or not) with the slides retracted. On some RVs it is very hard or even impossible to reach the bathroom or bedroom without at least partly deploying a slide.
I'm not sure I'm qualified to really suggest certain brands. I would give more care to checking condition (overall maintenance, freedom from leaks, etc.) than to brand, though of course not to total exclusion. Most of what you'll find is of course on a Ford chassis, and most of the rest on a Chevy chassis; both are generally reliable and should give little trouble with reasonable upkeep. Differences (and potential problems) are more to be found in the house part of the RV.