a very tempting offer. This is a brilliant strategy, and I am sure this strategy will be successfully caught the attention of many investors.

Yeah, just ask him. Don't give out his password. Maybe if you know it you should check (have you ever snooped before on him, and why do you know his pass?).

I can see your problem, I've had this VERY simmilar issue come to me before, ultimately it's your choice to snoop or not, This is where you make your choice, do you break a boundary by sneaking into your brothers personal life and reading his private facebook account data and relay it to your Inlaw? Or do you give the password to the girl, further erroding the privacy/trust bond between your brother and you even more than the previous mentioned idea?
Perhaps the right choice is to Stand Back and not do anything, That way you're not at blame for "things happening" however you could be blamed for "doing nothing" HOWEVER, you doing something requires you to access an account that does not belong to you, an account's private data belongs to the owner of the account (or facebook, I dont use it, fk them)

So, Do you Steal and Relay information "for the greater good"?
Do you Give away a Stolen password (i don't care how you got it) "for her"?
Do you stand back as an innocent bystander because you would have to break a technical law to "do something"?

You can obviously see wich of the three choices i picked.
Have a good gamble!

Just man up and ask your brother "Are you still with (sister in law here), are you seeing someone else?"

 and ghandi, and martin luther king.. you see all these public heroes, and you begin to question everything. it's a vicious cycle. sometimes i have to ask myself if i'm being too cynical, and i don't know what the answer really is. all these people that we've been told to worship are still human beings after all.

Try it and let us know if that worked for you. Also, it's a good idea to avoid using your laptop if it's not updated.

Well what did the other messages say? We/you need more context. If they were:

Brother: I just saved a bunch of puppies from a burning building. Do you want to meet up so I can give you one?
Girl: You're adorable. How soon can we meet?

Then no. But if:

Brother: I want to bury my face in your beautiful ass
Girl: You're adorable. How soon can we meet?

Then yes, he is cheating.

Brother: I'm really cold.
Girl: Me too
Girl: I'm wearing close to nothing. I'm freezing.

Then no. But if:

Brother: What are you wearing, you dirty little fucking skank
Girl: I'm wearing close to nothing. I'm freezing.

Then yes, maybe suspect.

And I wouldn't stick up for my bro if he was cheating. People have a right to know.

I'm generally an empathetic person person even if I don't act like it but when you actually look at the situation rather than going "Boo hoo that poor victim" I find it very hard. For one thing as people have already spammed in the comments of this article he got a 15 year old girl pregnant so he isn't exactly the shining beacon of intelligence and responsibility. For those internationally especially in America this is the kind of shit we have to put up with in the UK on a regular basis and the amazing thing is throughout all of it they manage to act completely indignant about the problems they have and blame everybody else so if you think we're being mean it's because we've seen it so many times we're wondering why the hell people don't learn.