I was pulling my hair out trying to remember a book series today with exactly the scenario that you describe. I stumbled into this webpage while I was searching for info on it. Except I remember the series being much older - I read it from my primary school library at about 1992.
A few minutes ago I suddenly remembered the name of the alien invaders in the books - the Tektrons. Just did a search, and the book series was called Counter Force, with 2 books in the series: Beware the Tektrons and Find the Tektrons. Authors were George Erskine and Ian Cameron. Published in late 80s.
Hopefully this is what you're searching for.
Edit: Being asked to provide more details about the series to see if they match the details in the question.
It's been about 30 years since I read the books, so I can't recall the series in full detail. I remember that the books were set in near future, but can't remember when. In each book humans were building a different high tech complex that Tektrons were planning to take over and invade the world with. They lived in the electronics/electricity and I think (not entirely sure) that the Tektrons were subtly pushing humans to build each complex for them without the humans knowing. Each book was a race against time stealth mission for the teenagers to destroy the complex before it goes fully operational.
There were about 5 or 6 teenagers. The main family, whose father went into hiding, and their friends. No-one knows about the invasion except father and the kids. The father sends encrypted messages to his kids at start of each book to give them their mission to infiltrate the compound the aliens plan to take over, and provide them with tech to defeat the aliens. I think 2 of the teenagers were genius-level tech nerds who decipher the coded messages and could build some of their tech. I don't think the father appears in the books, he goes into hiding before 1st book starts.
Can't really recall any details about the kids and their personalities!
