Why not just ask her? Seems to work for quite a few things and maybe she might already want to do it, but at least it is out in the open. But be careful what you wish for.....
If it works for both of you i.e. if she'd like you to either watch or wait somewhere else knowing she's with someone else and you'd like either or both of those scenarios - then it's a formula for...
This is not a desirable thing. To be a cuckold means your wife is having a lover behind your back. But if that is the masochistic buzz you are seeking, it should be not be hard to find a male friend...
You can be. If your sibling or cousin marries your wife's brother's wife then yes you are related. But there's no other way you could be related to them besides that way.