Complex sentence: Snow tries pushing away his advances, but he's very determined to have her and plans to kill Bigby and all of the children she had with him, and also plans to make her replace the children with their human children.
Split into simpler sentences: Snow tries pushing away his advances, but he's very determined to have her and plans to kill Bigby and all of the children she had with him. And plans to make her replace the children with their human children.