In UTH, how are the houses which you are going through decided? Do you know which houses they will be before going in to is it random/what’s available that day?
They're predetermined by Universal. When people start posting their UTH reviews listing houses, you'll notice that they are the same for everybody like 80% of the time. If a house is undergoing significant modifications that day, they'll sub in another house so now and then there's a little change.
From past experience, I would say that Ghostbusters and Stranger Things will be the "anchor" houses. If you do the 6 house tour, you'll definitely see them both (barring extensive work on them that day). Then one will probably be on the AM 3-house tour, and the other on the PM 3-house tour. They do that to try to make sure everybody is happy seeing at least some of the main houses.
If Depths is really claustrophobic / having narrow rooms/halls, they'll probably not have it on the tour as it's hard to have a big group in a space where everybody can see what the guide is pointing out. If one of the originals has a jaw dropping indoor facade, you can pretty much assume that it's making the 6-house cut.
Your best bet to see any particular houses you want, is obviously the 6 hour tour. In addition to seeing twice as many houses, they often give you a "little extra" like make sure to walk by the other houses so you can at least see and photograph the facades, for American Werewolf in London we were "snuck" in the exit and were allowed to pose for pictures with the last puppet with the tour guide taking your picture for you, and houses that share SS's they'll often say something like "we're not doing the other house in here, but the easiest exit is on the other side so we'll walk through here" and you get to see some things and snap some pics. One year they also asked if we wanted to break for lunch, or if we'd rather see a 7th house (we all obviously chose that) so they added one to the tour.