How do I go about soldering these plugs back on?

You are going to need to remove the plastic housing and get down to the board level. That should give you more room to get a nice wide chisel tip soldering iron in there. It will also allow you to see how the other surviving female posts are connected, as some ESCs also use a mechanical means (i.e. screw, then solder)

Ive got them tore down but I wonder if my 60w iron has the juice to do it and I hope I dont melt the board

this is a problem that some of these speed controls tend to have if stress is put into the wires. As said, remove the board, and use a high watt iron with a chisel tip on high heat settings. just tin each and solder back on (as these are soldered on)

60 Watt is plenty for this job. Just remember to use Flux sparingly to distribute the heat more efficiently and evenly and it should solder just like factory.

I would lightly dip the end that solders down to the board in flux and position it perfectly before applying heat and introducing solder so it will seat perfectly. Just make sure you're using a CLEAN chisel tip and quality solder.