Boundaries? What are those?

Back before my in-laws purchased their vacation home nearby, they used to stay with us when they visited.  That's where I became fond of the saying, "Fish and Family start to stink after 3 days".  

There were times I would run errands while the in-laws stayed home at our house.  That's when I learned that when I was out, my Mother-in-law would get on my computer and read my email.  Now I'm not sure how long she had been doing it, but one day I came home to find her quite upset.  

Sidenote: My husband's brother is a big time jerky jerk. He's pretty much a carbon copy of my Father-in-law.  We loved the brother's wife, but as any self-respecting woman who is being forced to live in a 1940's era marriage, she left him.  After the divorce we kept in close contact with her and she continued to come out and visit us.  

Now back to my MIL and why she was upset when I arrived home.  She had seen (and read) an email from my former sister-in-law to me.  It was a harmless email (i.e. it didn't say anything negative about the in-laws or her ex) but my MIL was pissed that I was still in contact with her.  Of course to confront me, she had to admit that she had been reading my email.  

She didn't seem to think that reading my email was as big of a deal as the fact that I was still in contact with her former daughter-in-law.  

Of course that day I immediately password-protected my computer and we then informed her that if she wanted to use the internet, she had to use the "guest" account on my husband's computer.  (by the way, she never even asked to use my computer prior to using it.)

This is the same woman that even now that they have a vacation house nearby, comes over to my house, sees a pile of mail, and will pick it up and go through it.  Ahhhhhhhhh!

Even though we don't play their games, my husband and I aren't really free to confront/reprimand them.  For one, it's against their culture to reprimand your elders, especially your parents.  And two, with their emotional maturity of high-schoolers, if we were to ever reprimand them... they would sell their vacation house and never visit/talk to us again.  While that is sometimes a tempting option, in the long run we feel it best not to get cut off by the family.  

So my husband and I are forced to just complain to each other about them.  We actually text each other under the table when we're eating with them, or my husband will grab my knee whenever they are saying something ridiculous.  

Thank God my husband is just as annoyed by them as I am, or I'd never make it!