Garden Pests and Diseases: Help! Are these aphids? All over mandarin tree, 1 by Vadla

Vadla wrote:
Some insects are all over my mandarin tree!
I've looked through some posts and they look like they could be aphids to me. But I don't know very much at all since I'm fairly new to gardening. What are they, and what am I supposed to do to stop them?

There is also something growing in another tree of mine which has "webs" that are fairly large maybe 15cm in diameter.

I've added photos of both, any help with either or both of these would be greatly appreciated!