Can a cosigner sell without primary owner agreeing?

Check your Deed. If you both are "undivided" owners..meaning you both own the property equally 100%..then NO they can not sell. Most of the time there is rights of survivorship in that kind of Title but if you each own 1/2 or 1/4 or ???? "divided interest..they can sell their share... 1/2 or 1/4. Check with your closing attorney.