Using a network drive for multiple backups has some complexity to it, and you are not likely to find an article that spells out all the twists and turns.
In addition to locally-attached backup drive, you can backup to:
• a network drive connected to another Mac (I use an older Mac located in the basement as a server)
• a Time capsule (but that is kind of obsolete)
• a network-attached storage (NAS) device that is compliant (that is essentially another computer that may not be a Mac)
• a drive connected to certain compliant Routers.
But a fundamental rule is that you can't get 2 TB of **** into a 1 TB bag.
My recommendation would be to continue to back up your wife's computer using the Time capsule, for as long as it continues to work for that purpose. That way she can do what she wants, and does not have to fret about a backup.
Meanwhile, find another solution for your computer, that may or may not incorporate the data from your wife's computer at a a later date.
Aafter you have given it some thought, readers would be happy to talk more about options.
Important things to know: you are not limited to ONE time machine backup drive. Also, you can have a local as well as a remote drive for your backups. Each backup drive creates a stand-alone backup, and continues until you retire it.