Not sure what the first one might be...but the second picture could be scale? Possibly the third picture "might" be black aphids?

Google and compare pictures to your pest...Good luck!!

Here is a link that might be useful: Picture of black aphids

Maybe a fungus, especially if it doesn't wash off. However, the one picture looks like some bug has laid eggs in a cluster form. They may hatch into little worms. But if eggs, you would be able to scrape them off.

Just so you know, a lot of Hoyas can develop black spots when kept in very strong light, and that is nothing to be worried about.

In this case, the spots are definitely problematic, because it is widespread and there is yellowing around them. I agree with mairzy that it looks fungal, or that at least this is a good starting diagnosis.

There are a lot of different ways you can treat such an infection. I'm not sure how widespread your situation is, but if possible it's always best to start with the gentlest treatment and work your way up, if needed.

You can begin with a natural remedy and make a paste out of cinnamon and water and smear it over both sides of the spots. The spots should 'dry up' and be more solidly black, with no more spread, if this works.

A harsher but stronger method is using chemicals, such as spraying the affected plants with a Physan 20 mixture (2t/g) or an alternate fungicide.

Another method frequently mentioned is to use athlete's foot spray. Some people just mist it in the air over the tops of their orchids and let it settle on the leaves. I've sprayed it directly on a Hoya leaf before and it didn't seem to cause any harm.

Good luck :\