Is this possible?
In theory yes. But, you would have to open up the Time Capsule case, pull the hard drive, install it in a separate enclosure, partition the drive using Disk Utility on your Mac, then re-install the drive again.
This is a ton of work, and not easy.....not to mention that it will void the warranty, if in effect.
If you do nothing, Time Machine will automatically keep the backups of each Mac separate. That should be adequate for most users.