Once I get to Heaven, will I be grieving that certain family members won't be there?
In Heaven we will all be surrounded by family, because of our essential identity as brothers and sisters, sharing a common Father. This is not a “pretend family,” but a very real one. It’s not that God merely uses the earthly family as an illustration of His eternal family, it’s that earthly family was designed after the ultimate, it’s but a model of the real thing in Heaven. (Sometimes the model is very good, sometimes very poor, but never is it as good as the ultimate thing it was made to reflect and point to.) Jesus spoke of family relationships that go far deeper than blood relations.
While Jesus was still talking to the crowd, his mother and brothers stood outside, wanting to speak to Him. Someone told Him, “Your mother and brothers are standing outside, wanting to speak to you.” He replied to him, “Who is my mother, and who are my brothers?” Pointing to His disciples, He said, “Here are my mother and my brothers. For whoever does the will of my Father in heaven is my brother and sister and mother” (Matthew 12:46-50).
In Heaven Jesus will wipe away our tears and there won’t be any more pain (Revelation 21:4), so we know we will not be gripped by remorse at anything, including the fact that certain family members from earth aren’t there. We will have an eternal perspective, we will know that God has been just in His judgments, and will not be plagued by doubt. Naturally, we can’t imagine that now, but that’s because we’re not in Heaven–far from it! When the child is in the womb he can’t imagine what awaits him on the outside, but it’s true nonetheless.