In the Mormon Religion when a married couple get sealed to each other does that mean if one of them commits A Serious Sin like murder both of them will go to hell for it?

Answer 1

No. The Temple Sealing is only valid of both the man and the woman keep the promises and covenants they have made both at Baptism and in Temple Ordinances. If someone does not live up to the promises they made with God (such as keeping the ten commandments or obeying the law of chastity), the promises given to them by God (admittance into heaven, being sealed to your spouse eternally) are no longer applicable. In this case the sealing is broken unless the one who broke it sufficiently repents. The other member of the couple will receive all that was promised if they continue to keep their covenants, and will have the opportunity to be sealed to another spouse either in this life or after death.

This is explained in Doctrine and Covenants 82:10, which says "I, the Lord, am bound when ye do what I say, but when ye do not what I say, ye have no promise."