A) They don't seem to be doing anything meaningful, other than avoiding in focus cameras and the occasional capture-anal-probe-and-release of a few people. We may be a subject of study, but the impact is about as much as Jane Goodall had to the primates she sat with. If anything, bet that the Earth is a quarantine zone.
B) If they are planning an invasion there is zero we can do until they commence hostilities, in which case we'll go with what we got and make up the rest as we go along. We're a resilient and numerous species that may be a whole lot more than a distant people can bite off, let alone chew.
I don't subscribe to the notion that governments are working in secret with Space Aliens; governments do a lot of things well, but one they absolutely suck at is keeping secrets, or having their secrets remain hidden after they fall.
I do like the Ancient Alien theory that people were genetically engineered to be slaves to Space Alien Overlords but quickly turned the tables on them and so they left. That would make us the assh*le species of the Universe, and that appeals to me on so many levels.
The opinions of this poster are largely based on facts and portray a possible version of the actual events.