AJ:
Good afternoon. To answer your question about subst. olive oil for butter/margerine the answer is that you use 25% less oil: 1 TBLS of BUTTER/MARG EQUALS 3/4 TBLS of OLIVE OIL. I hope this info helps you.
However my friend, I cannot say how your baked product will fare due to the subt... I can understand your concern about your health, however, if you do not consume an overly amount over the years I do not believe it will harm your health. One more thing when using margerine for baking purposes "ALWAYS"...always use margerine that contains at miminum of 70% fat. I do not usually employ margerine but when I must I only the safest & the best there is use Fleischmans margerine it comes in a carton of 4 sticks just like butter & it is made for baking. When it is on sale I pay only $1.00 for the package.
Well, I hope info will help you make the proper decision.
Good luck & enjoy the rest of the day.

~CHEF DUNASK.