score:7
The short answer to this question is, "Yes", but the process is much more complicated than civil divorce. Breaking seals on marriages are considered exceptions to the rule, and are dealt with on a case-by-case basis.
Before a woman can be sealed to another man, the sealing to her fist husband must be broken. For this to be accomplished, the woman must begin the process by meeting with her bishop and explaining to him the circumstances for why she wishes to have her sealing broken. The bishop does not have authority to break a sealing, but can direct the woman and help her through the process. After a series of interviews these sorts of things eventually go all the way up to the first presidency of the church for review and approval. They determine whether or not the woman is justified in having her sealing to her first husband broken. One of the only circumstances for which a woman may have her sealing broken to a deceased husband is if she wishes to be sealed to a new husband.
For clarity: civil marriage, and temple marriage (being sealed) are distinct in that a civil marriage is "Until death do they part" (for time), whereas a temple marriage is "For time and all eternity" (for eternity). A woman who is sealed to her husband--but later remarries due to death or civil divorce--retains her sealing to her first husband. If the sealing is left intact, then after death she is parted from her second husband and rejoined with her first.
Upvote:2
Let me address your #3 separately.
There is a difference between a sealing between husband and wife, and a sealing between child and parent.
Sealing husband to wife seals them in marriage for time and all eternity, so long as that sealing is itself sealed by the Holy Spirit of Promise, a unique function of the Holy Ghost that ratifies the sealing of husband and wife. In other words, the earthly ordinance isn't magic. For the unrepentant, a temple sealing is of no greater value than a civil marriage.
Sealing children to parents is a bond of responsibility. The Church teaches that "families can be together forever." But, once again, the ordinances of the Church are not magic. Unrepentant children will not follow their righteous parents to the Celestial Kingdom. The sealing of Children is in partial fulfillment of the teachings of Malachi when he said,
Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the Lord: And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.
If a daughter is born to parents who have previously been sealed in the Temple, then she is "born in the covenant" and her sealing to her parents is automatic. If the family are converts to the Church, then the sealing of children to parents is performed.
In the case you suggest, the sealing of daughter to mother was never interrupted. The daughter's sealing to her biological father was also never interrupted. It is unusual in the Church to re-seal adopted children to adoptive parents, unless there is a pre-existing issue such as abuse. This is especially true for adult children.
Simply said, the sealing of children to parents is actually quite separate from the sealing of husband and wife, and only rarely does one affect the other.