Yes. Subscriptions to MSP support 4 administrator installations, and if needed, more can be purchased by going to MSP's License Login page and next to where it says "Maximum Computers:" click the "Expand" button.
You can now select how many computers you need with the "New maximum number of computers allowed" drop down. You can also add more volunteers or upgrade to the Plus Edition from this screen. After selecting your options, click "Continue" and you will be given a price breakdown, and can choose "Continue" again to be brought to the payment screen.