This is a place where we indicate inconsistencies and discuss them.
If you don't want to examine this area of your ideas, that's perfectly acceptable.
If your descriptions are accurate, I've no doubt that this family has an inclination towards trouble and you should stay away from them.
But statements like this are just interesting:
Having known these people for years, I can confidently say everything about them is white trash. Before I met them I had no idea there's a family out there that actually resemble the stereotype.
Of course there's people that resemble the stereotype. If there wasn't anyone who resembled it... then it wouldn't exist as a stereotype.
There's plenty more than just this one family.
But, which is it? Do they just "resemble" the stereotype or is "everything about them" the stereotype?
You're the one choosing to speak in absolutes about people.
Any absolute statement you say about people isn't going to be true.
"All mothers love their children." -not true
"All rocket scientists are smart." -not true
"Nobody wants to die alone." -not true
That's how I can tell that you're wrong when you say "everything about them is white trash." Of course it isn't, that's just immature and dismissive to say such things.
If you're interested in getting to the bottom of any issues your boyfriend has with his family, then dismissing everything about them isn't going to help the two of you communicate about the concept.
If you're interested in getting as far away from the family as possible, dismissing everything about them won't allow you to anticipate anything they do correctly and you'll end up running into them again and having more problems.
Either way, dismissing the truth entirely isn't going to help you.