It's really hard to see what's dented. If the rear damage is only on the top, just fix it.
If the sides of the fenders are pushed in and the metal is stretched, it's gonna be a pain to get behind those areas to push them out and lay flat.
Ask me how I know.
Use 2 cars to make one good one. The best parts go on the keeper and the worst are spares.
I swapped front fenders on my car for 2 reasons. One, the rain gutters in the fenders corrode. Pull up the hood seal to see if that makes your decision. Two, there are parts of the front fender (towards the rear of the car) that are double walled and don't respond well to repair. The double wall design also rusts easily. If rusty, swap them out. Had mine dipped.
Dunnow whats wrong with you MIG guys.
My Miller makes any welding a piece-o-cake. Once you learn how to run one, burn through and blobbing is hard to do.
Coupla rules on MIG welders for teeners with thin sheet metal.
One. Use gas and solid wire, not flux core wire.
Two - buy a good one with with INFINITELY
adjustable feed and volts. Use very low voltage settings on teeners.
Them 4 setting voltage thingys just won't cut it.
Three, take a 2-3 inch long piece of copper pipe, pound half of it flat and secure a wood dowel into the open end. Place the flat part of the pipe directly behind the weld area (bend the flat if ya have to) and have at it. The weld won't drip through because there is a copper backing behind, the copper acts as a heat sink and makes it seem like the metal is thicker.
Oh yeah, a light touch, tack welds, the right backing, and the right settings go a long way towards success.
Ken