Having twins or two kids is a wonderful thing; everything learned in the case of the first child can be brought up and used for the second one. Also, another child requires more space to play, to eat, to learn and to sleep.
If you don’t have enough space available or if the sister occupies the second bedroom, the best way to think about it is creating a bunk bed or two floor beds. Two kids…double up the space on vertical.
Think that the functionality of the room may change if you have twins or brothers (sisters). In the same space as before you need to fulfill the desires of two children. That means two beds, two dressers, two night lamps. Don’t treat your kids to fancy, in the case of bunk beds, a night lamp can be deployed even on the top with some improvisations like mounting a shelve on the wall near the bed or mounting a light variation light near it.
For functionality to be at its best, try making two small dressers than a big one to keep them off conflicts and maximize space in the room. Consider that the mood of the room helps them in daily activities, the bunk bed can be a sort of a mini gym, and kids can hang over and practice. Also keep it organized, buy some boxes for them to put the toys in. Make sure that the color of the bed is associated with the rest of the room.
The kids may have a small social order; in this case the “big brother” may want to sit on top of the bed. Yes, let him sit there, but you must comfort the smaller one that “living downstairs” has more advantages, therefore making both happy.
Conflicts may rise if you have two kids sharing the same room, keep up with them, respect their wishes and if Bobby wants the room painted in green and Charlie wants it in blue, talk to them and come over to compromise.