Cheaper to stay in one or two rooms?

I will be traveling to Japan in November for 10 days. I've talked to a travel agent before, and have done my own research, and both have led me to believe that the prices you pay at a hotel are dependent on the amount of people, not the room style. Here, one would pay a flat rate for a triple room for yourself and two others to stay, whereas in Japan they price the stay per person. My question is, is this correct? I would like to have some space from my two family members I am traveling with (partly because they snore) and am wondering if it would indeed be cheaper or at least about the same price to have my own room.

Only Japanese style inns (ryokan) charge by the number of the guests. Hotels go by room types, but the three persons in one room costs more than two peoples in one room.

It's cheaper to get a room for three.

I've talked to a travel agent before, and have done my own research, and both have led me to believe that the prices you pay at a hotel are dependent on the amount of people, not the room style. Here, one would pay a flat rate for a triple room for yourself and two others to stay, whereas in Japan they price the stay per person. My question is, is this correct?

It depends on the type of hotel. Japanese inns and business hotels typically charge by the person, and the per person rate decreases with each person added to the room. While western style hotels often charge by the room instead (typically with limit on the number of guests in a room)

I would like to have some space from my two family members I am traveling with (partly because they snore) and am wondering if it would indeed be cheaper or at least about the same price to have my own room.

Almost certainly not if you stay at a ryokan (Japanese inn). Assuming the ryokan even allows single guests in a room (many do not), it will be cheaper to have three to a room as the per person rate get cheaper with the more guests that share a room.

Business hotels are a different story. Many do not offer triples, so a double and a single may be the only option.

And it would obviously double your hotel costs if you stay at Western hotels that charge by the room.