How to power 5 x 1.5v dc motors from uk mains
You could use a 7.5Vdc power supply if connected in series. (Daisy chained)
Or you could connect them all in parallel using a 1.5Vdc power supply.

Knowing what you are using them for would help. Is the load on the motors changing? Etc.

The main thing is knowing what is the current draw for each motor is, so you can make sure your power supply has enough capacity to power the system.
Power = Current X Voltage - in Watts

You should not have to worry about safety, especially once the current draw to the motors should be, and adding a fuse to be sure. Example: if the motors draw 1 Amp, put in a 2 Amp fuse. Or a 1.5 amp slow blow. Motors have a high start up current, so I would recommend the slow blow fuse.