If I write an autobiography and include living family members who have done some very strange things, am I at the risk of being sued?
If you're in the US, perhaps. What might be better is to label it semi-autobiographical, say "based on true events", and change the names of the characters. I believe you can also include the portion that films/books sometimes include:
Any resemblance to actual persons, living or dead, or actual events is purely coincidental.
Some additional suggestions and useful verbage here: https://www.thebookdesigner.com/2010/01/6-copyright-page-disclaimers-and-giving-credit/
You may want to check into Lawyers and Accountants for the Arts as well; they have a full guide on copyright that I believe is a free resource.
[Standard Not A Lawyer proviso]
There's always a risk of being sued, and you might want to avoid that hassle entirely. Morgan's suggestion is a good one, but if a real person can be judged to be recognisable from a character there might still be a problem. What's probably more significant is whether you're at risk of being successfully sued.
Libel laws vary between jurisdictions, particularly concerning whether burden of proof is on the plaintiff or the defendant - an example that often comes up in legal dramas is that the UK and US see this the opposite way. You'll want to check this wherever the book may be published or distributed.
If you have proof that what you've written is true you'll have covered your back, but it would still be worth talking to a qualified legal advisor to check that your proof constitutes something that would be recognised as legal proof.
The basic legal principle that applies in all jurisdictions is that if you want to publish anything personal about anyone, you have to ask them. This includes data (name, birth date, life events, etc.), likenesses (photo, drawing, etc.), and communications (letters, writings, personal communication etc.).
If you want to disregard that law, you should make damn sure you don't disparage, vilify, slur, denigrate, libel, sully or defame that person in any way whatsoever, as that will add to the damages you will have to pay.
If you want to ignore that law also, make sure you are rich before you publish your autobiography.
There are some exceptions that apply to art, but I wouldn't count on your outpourings to be considered art by a court of law.