rights of second mortgage lender

I have a first mortgage that I refinanced 4 years ago. Since the refinance I have never been a day late on my payments. However I have a second mortgage that the bank would never work with us. They recently sold the second to another lender.
From research I found the second is very aggressive and hard to work with. My first mortgage is far under water. Probably 8-10 years before there is any equity. I am not paying the second at this time. I know the threats are coming from the second lender. what can they legally do other than try to work with me. thanks george

From research