My Beta Readers

I have 4 beta readers. Sometimes, if I’m lucky, I have 5. These are the people who read everything I write once it’s completed and before I send it to my agent and then hopefully to my editor.

These people are not certified beta readers.
They are all big readers across many different genres.
They are all family, so as another writer I know recently revealed I don’t have to worry about any of them stealing one of my book ideas. The trust issue isn’t an issue.
One is my one-woman cheerleading squad. She’s the only person who sometimes reads along while I write because she is infallibly enthusiastic and supportive and probably one of the main reasons I ever finish anything. Without her, it is likely that I would give up halfway through when things tend to get knotty.
One is a university professor and a writer of non-fiction herself.
One is a reader of smart sci-fi and maritime historical fiction and non-fiction.
One is a 17 year old girl who reads YA pretty much exclusively. ‘Cause the other stuff is boring, innit?!
Between them I tend to get a lot of feedback and a lot of criticsm. If it wasn’t for them I would lack the confidence to ever send anything to my agent, who although he is totally supportive and a ‘Jo’ fan, is also incredibly busy wheeling and dealing for all his clients.
How do you choose your beta readers?