Now that we know you are exhausting toilets, the answer to your original question is "It Depends."
How do you intend to control the fan(s)? Do you need continuous exhaust or intermittent?
If the exhaust needs to be continuous, or at least operate only when the building is occupied or the ventilation system is on, then the answer is YES, a single exhaust fan makes sense.
However, if the toilets need only intermittent exhaust (on for only 15 min every hour), then one fan for each toilet is preferred. Not that you can't do one fan for both with intermittent exhaust, controlling them gets a little more complicated and you need to coordinate more with the electrical engineer.