Question 1 - Front
Placing Qs in the back row completes your full house in the back, guaranteeing the 6 point royalty.
Placing Qs in the front row pretty much seals your Fantasy Land fate (which is worth approximately 13 points as a buyout). You also have a redraw for that last 4 in the deck to catch quads in the back.
Question 2 - Front
Placing Th in the back row gives you 2 pairs in the back, going from a loss to both opponents in the back row to being ahead of both opponents. In addition, you could potentially scoop Villain 2 with this placement. Therefore, we can consider this move to be a likely 7 point swing (five points from Villain 2 and two points from Villain 1).
Placing Th in the front row does not endanger you from fouling and gives you the extra 5 point royalty from each player, providing a likely 10 point swing.