Hand 1 - If you're going to re-rasie here, you need to bet more...make it $30 - $35 straight. A re-rasie of only $13 (with 3-4 people already calling the intilal raise) is not going to get a lot of people out, and I don't think you want to be playing a huge pot OOP against 4 opponents. On the flop I think you have to call his rasie striclty due to pot odds (your getting well over 3:1 on your money).

Hand 2 : with a short stack, this is as good a spot as any to get your chips in the middle.