Up to 3 internal antennas can be connected to one booster, but you need to take into consideration that the internal antenna will provide you with 10 feet coverage (from antenna). And as you split, the signal will get weak, as you are not providing with better signal, but you are splitting the existing one.
In such cases we recommend our customers to provide us with their layout plan, so as we can recommend the right option. In most cases, two boosters are recommended to be purchased.