Siblings are not allowed to serve on the same ship; I assume that extends to the same unit too. This policy is detailed in "Left to Die: The Tragedy of the USS Juneau" (great read, BTW). That's the boat the five Sullivan brothers died on and also the four Rogers brothers. I dunno if the other services have a similar rule. The book, obviously, doesn't talk about married folks. I don't think the rule would be the same for other than siblings as the intent of the rule is to protect a family from losing all its children in one event.
I know 2 brothers have been in the same guard unit for some time now. They both fly for the 192nd out of VA.
Actually, I can think of more than a few guard units where they have siblings or the father/son relationship going on within the squadron. I'm pretty sure a few of them have been on the same combat deployment as well. (Though in the guard it's only 30-45 days, they split up a 90 day deployment between 2 or 3 units)
Not sure if that's just the JO spirit or the general brown shoe rebel streak. Sure, they got caught but huge points for just trying it.
Certainly some communities and some squadrons are tighter and some looser than other. Can't imagine that all shoes are uptight A-holes. Oh' wait, after 20 years of dealing with them I can 