There are some people who just don't like be passed and they get competitive when it happens (guys more than girls?). It is like when you are driving, behind someone slow and as soon as you try to pass, they speed up or make it difficult for you. I guess these people are everywhere.

On our bike path (or most places I imagine), the etiquette is if you hear someone coming up from behind, keep to your right if you think they want to pass. People are not supposed to right two by two, but some do anyway. They will normally go single file when they hear someone coming, but some die-hards just will not give it up.

Sounds like you have a couple of die-hards (or blow-hards!) on your hands. It's annoying, isn't it! Don't let them spoil your ride. I have run it a few of these. I keep smiling, am courteous, if my initial warning (bell ring or comment) is ignored, I state loudly 'hello, can I get around you please' when other efforts fail - I think they realize they are going look like real jerks if they don't let me pass since I am being pretty civilized about it.