In a small studio reflective umbrellas are hard to work with. It's tricky to control the light. But it can be done, and they have a great character.
If the studio is small you will end up with your key light source(s) close to your subject.
You don't usually want to light the model and the background with the same light. (Looks crap in most situations.) So you put the light close to the model and place the model as far away from the wall as possible. This way the light lost most of its energy once it reaches the wall, this goes quick! If you put the light further away the model and background will be more evenly lit.
You can also create some angle with the key sources, this will put more contrast in on the models, you can control this with a second umbrella on the other side, but this is two lights already. Than you can always add a different light for the backgrond.
In a small studio you will enjoy the softbox most since you want to reduce spilling. If you have to light bigger spaces go for the umbrella or more lights. But hey their characters are a lot different so this is just the easy way not the only one.