Following are some examples showing how various scenarios would play out under the current LDS church policies.
Scenario 1: A man marries a woman who already has three children from a previous marriage, ages 20, 17 and 15. When the children are sealed to this man, they are all in attendance in the temple. Two months later, the 20-year-old daughter is sealed to her husband in the temple, but unfortunately the 17- and 15-year-old siblings will have to wait outside.
Solution: The daughter could have the option of having a civil ceremony where all of her family could be in attendance.
Scenario 2: A 19-year-old girl is going to be married in the temple. Her twin sister will not be allowed to attend the sealing because she is not yet endowed.
Solution: The sister could have the option of having a civil ceremony where all of her family could be in attendance.
Scenario 3: A temple-worthy couple decides to have a civil marriage to include all of their family (many non-members on both sides). Because of their civil union, they have to wait one year before they are allowed to be sealed to each other. However, this does not invalidate their temple recommends so they may attend the temple and perform all temple ordinances including marriage sealings for the dead, but may not receive this ordinance for themselves.
Solution: Dissolve the one-year-wait policy.