aoch,
That is one sick puppy you have there!
Two things to do:
- Get rid of the critters
- Give your plant something to live for
If I look at the scale on the plant, you may be in luck; The ones you took photos of are already dead. When they are alive, they are like little caps pressed tightly against the leave. The fact that there is so much space between them and the leave, indicates the scale is dead. that does not mean there are no live ones though!
If this were my plant.. I would take a normal water spraying device (No clue as to what you cal these things!). Put in a good spoonfull of dishwashing soap (Actual soap, not the chemical fake stuff, best it traditional soft soap), and a shotglass of rubbing alcohol and fill with luke-warm water. Then spray the whole plant dripping wet. After half an hour, take the ficus to your shower and with luke-warm water wash her down completely. If a lot of your soapy water runs into the top, it might be a good idea to fill the washbasin with water, and put the plant in it after rinsing: This way you will dilute soap from the roots. Then drain the plant of the excess water. If you want, you can then water a little with liquid fertiliser, normal strength.
Place the plant out of direct sun but bright light, and out of the wind. It should recover just fine. Ficus Benjamina is very hardy.