2 prong to 3 prong electrical plug... Fire hazard or not?

The only time it might be considered a fire hazard is: 1 if the cables are damaged, run them through your hands and you can usually feel any damage in the cables. 2, if your overloading the cable, the 3 items would not overload the cable/extension 3, you have poor wiring in the house, if your lights or things flicker or go on/off when plugged in, I wouldnt use that socket. 4, damaged charging cable, again run the cable through your hand to check for damage.

5 if you replaced the battery in any of those items with a cheap or none regulated battery, eg you bought a battery cheap that was not made by Blackburry, these batterys can be a fire hazard. Really there is very little danger to charging your devices overnight on the same extension cord/plug socket. Just don't place the devices on your bed or other soft/insulating surface as it can heat them up (and the chargers).

It depends my whole room is power via extension leads cause it only has 2 mains plugs however If the extension lead has a fuse or surge protector it has virtually no chance of catching fire because if it overloads the fuse cuts out stopping all power plugs have these too to stop overcharging and overheating hoped I helped I'm 15 and still alive so it should be fine but ask your dad if it has got a fuse in the actual plug box be safe and check.