can you and another person share Polar Ft4 or Ft7?

Hi there!
You'll be better off, buying an individual HRM for each of you (chest strap/sensor plus watch or some models have a chest strap/sensor only and connect to an individual smart phone, like Polar H7). Each HRM sensor transmits on a dedicated frequency to the wrist watch (or phone) to avoid interference. You will have to enter your respective vital stats into the wrist watch (or phone app), such as gender, age, height, current body weight (has to be updated, in case you gain of lose weight). Your results will not be the same as your husbands for that reason.
The little computers also keep your workout log. If you keep changing the data when you switch the wearer of the HRM you might lose your workout history.

Happy training!