from what you said, and being a mother, I would interpret it more from your mothers position. it has more to do with age. a girl is after her babies. that is hard for a mother to take. you said you were never involved much with girls so that is why she didn't respond that way to you. but she was consistent that way with your brothers. it will probably last longer with your youngest brother because he is the baby of the family. I always saw all my sons girlfriends as trying to take my son away from me. I didn't respond as your mother did. but it is a natural response. my son has been married for like six years and still when I encounter his wife, I feel a bit of resentment, like he is mine. and she is a great girl. so your mom is taking it a bit far by being a ***** and calling them trashing names, but her feelings are normal. she just doesn't know how to deal with them.