EDIT: on second thought (i'll leave my original reply below, so you can read it and use the information in it after you fix the big problem) i noticed while looking at the schematics a second time: you have 12V lamps on the secondary. these will have a very low resistance compared to a 220V lamp. the very low resistance could be what's loading the secondary down to 60-80V.
solution #1, change lamps to 220V
if the problem persists after that, read my original response below:
first, measure the 12V at the center tap of the transformer when you have a lamp on the secondary. if the 12V supply voltage drops when you connect the lamp, you need a beefier 12V power supply.
if the 12V stays the same (or drops less than 10%) put a second set of FETs in parallel with the ones already there, and use a higher wattage transformer. you don't need source resistors like you do with bipolar transistors, because FETs don't do the "current hog" thing like BJTs do.
What is the light bulbs? (voltage, current, watts .... any data)
What information do you have on the transformer? Winding resistance?