MGlitch's advice is the best. It really seems that you and your husband's accounts have been cross linked. Log into Overdrive.com and delete all your saved libraries (
https://www.overdrive.com/account/libraries). Then log into the Libby app and remove all your cards. Tap on the middle icon (≡) at the bottom and then select "Manage Cards". On the individual cards, select "Actions", and "Remove Card". Once you've done all that, log out of Overdrive on your Kobo reader.
Have your husband do the same steps. Once you both have finished, then start adding cards back to Libby. When you log into Overdrive on your Kobo, use your Overdrive.com login. The library you first add to Libby will be your main library on your Kobo, I believe. Or it may be the one you select when first setting up Overdrive on your Kobo. It's been some time since I've done it, so I can't recall. Kobo may support multiple libraries through Libby, but on the actual reader, only the main library is linked to the Kobo store. I hope this helps.