For me, I like dual backups, one on an attached drive and the other on a TC in another building. I tried to use a synology NAS at one point (maybe two years ago) for TM backups, but found restoring somewhat scary and unreliable... not that a TC is completely reliable.
Another idea since you never plug the laptops in is to use a cloud backup like Google Drive or OneDrive to constitute an offside backup in addition to the Time Capsule. That way it is completely seamless and wireless. Plus, with the incentives offered today with hardware purchases and upgrades I scored 115 GB of Google Drive space by buying a Chromebook to use alongside my Mac. It works great for hosting and sharing files as well as backing up data in addition to my AirPort Extreme with a USB hard disk.