okay, have a good nap, you must need it! so here's some dirt on perceived cabinet volumes:
the 2x12 will distribute/project your sound less distance but still be technically as loud using normal measuring practices about a foot from the cone if the speakers are the same efficiency and basic response curve... now putting lower efficiency speakers in will really give you some dropping as every 3dB decrease in efficiency will provide a 30-50% volume cut per watt at 1 foot from the cone (its a logarithmic scale, so the 1st 3dB cut about 50%, then an additional 3dB down is 30 or 40% quieter measured at a foot but really you won't find speakers lower than like 95dB, median is about 98dB, though there's some swing in different manufacturer's specs due to different measuring conditions and outright lies to make their product appear more robust on paper).... you couple in the 50% less projection from the smaller enclosure and it should really help with the neighbors
you have some fender speakers (probably made by eminence) and an EV right now, right? Emis, even the OEM models, tend to be pretty efficient and EVs are hugely efficient speakers with long throw cones (designed to maintain or increase efficiency at distances greater than 1 foot). You probably have a system efficiency of about 100dB or so depending on the fender speaker specs. If you look at speakers with a 98dB efficiency (medium magnet ceramics and Jensen style alnicos with higher handling) you will be getting some volume cut even close to the cab while still working the amp hard internally the way tis designed to be run.... if you go down lower into light magnet turf you will be knocking a lot more volume off, but you will need at elast 100 watts of handling for safety really limiting your options. Weber speakers DT series designed for Derek Trucks comes to mind and may give you the more American tones of your current rig, but in sub 98dB speakers my favorite is the 80s Celestion G12S50. I like the even lower efficiency 80s G12L35 too but 2 of those won't handle your amp with all 4 tubes in and you will have to pull a pair of tubes and halve amp impedance to avoid blowing them. And at 50 watts the 35 tends to break up prettye arly, get growly, and you might not like that given that you like EVs whch have late distortion even when pummeled (and handle 300 fucking watts)....
so with similar speakers in a 2x12 it won't sound quieter to you (though maybe darker as the cab is shorter and not blasting in your ear when sitting on the floor), but it'll be a little quieter to your family and a good deal quieter to your neighbors, maybe not enough for everyone's comfort though.... using really inefficient speakers (sub 98dB which is greenback level as well as a lot of other classic designs with decent power handling) may drop you down low enough though wen you factor in the reduced projection... given you are a 100 watter your choices of low efficiency speakers are somewhat limited, as I mentioned, given that most manufacturers never made a low efficiency speaker with 50 watt+ handling because low efficiency used to be considered a budget model back when everyone wanted to be louder and louder
that help?