@Philippe252 well, it is your decision whether you want to make it simple or complicated. Based on what you want: renting room 1 by itself and renting room 1 and 2 together with different prices when needed, it is going to be a homework to keep this in 1 listing and people most likely think that they automatically getting 2 rooms with the price.
The thing is, there is no option to add an extra $ automatically for people who want the 2nd bedroom (the only option is to add additional $ for extra people), so not sure you are able to charge extra $ automatically for let's say 2 people who wants both rooms. You can always add additional fee afterward, but that means you need to make sure that people are aware and you are on top of it.