For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Sin is in essence rebellion to God. God does not want sin to exist but He does allow it to happen, in part because He values free will for us and He gives us the choice to follow Him or to disobey Him.
I suppose if you want, this question can be rephrased as, "does God value sin more than He values free-will?" By giving us free-will, He understood that we are given the ability to disobey Him. That we have a choice between life and death.
I am a parent. I don't want my children to love me because I commanded them to. I want them to love me out of their own free will. This means I must let them choose, even if its a decision that goes against my favor.
Your choice now is to love God back (Matthew 22:36-40, 1 John 4:19).
Where is free will to sin in heaven? How did you think Satan managed to rebel against God? It's his free will. Satan chose to rebel against God.
I'm totally not following your line of reasoning with regards to babies.
Perhaps the answers listed here will help you.
Do the souls of aborted babies go to heaven?
As for the rest of your questions, the Bible is silent on these issues, though we can probably infer based on God's attributes. In the end, its speculative at best.