Yes you can use SoG to rescue the other half of the two liner, but you do not get two LS's. One goes to the person who first rescued it and the other goes to you. so be careful because if they are at 4 LS's and you rescue the other half, then they win because their half of the LS now counts.
also once the two liner is rescued if any player who owns one half of the two liner has a GoYS in play, then that LS cannot be targeted with FA. even the half that is in an unguarded LoR.