I feel something needs to be said and no one in the 7 pages of this thread has said it: Don't burn your bridges with a family that obviously cares about you.
Are their actions out of line? Extreme, maybe. But I can see that what they are doing is only because they fear they will lose you. Is your mother normally like this? what is your relationship like with your mom besides this?
Everyone is encouraging to cut ties, move out, etc and while you DO need to establish yourself as an adult, not one person has said anything to the effect of being careful to not destroy your relationship with your mom.... because she is your mom, at the end of the day.
The reason I say this is because in all likelihood your relationship will be fine and you two will be happy together and your mom will grow to accept this in time. But look at the other eventuality: if you burn your bridges with your family and then this guy whom you havent even met yet turns out to not be what he says he is, or the relationship doesnt work... who will support you in the aftermath? Who will be there the love you unconditionally? Im not saying this will happen, I'm just sayig you need to weigh up your options and tread carefully.
Most of us are lucky, we never had this problem. However, I know in my heart I would've never sacrificed my relationship with my parents for a man I hadnt met. Never.
I think as you suggested, him coming to the US first is the best idea. You will be able to be in a safe environment which will put your mom at ease and even give her the ability to meet him in person.