If you can safeguard your chastity without remarrying, then you do not have to remarry. In this, it is still advisable to remarry as it is Sunnah. If you cannot safeguard your chastity, then you should remarry. It is not necessary to stay with your deceased husband's family. Furthermore, if there are no provisions for Hijab (headcovering) and Purdah (proper women's dress) while living with them, then you cannot live with them.