How many instances have there been in the sport's history

...wherein relatives have moved through the rankings of the same sanctioning body in the same weight division and been asked to do battle with each other?

First off, let's clear up - how many times have relatives (we'll restrict this to nuclear - ie brother vs. brother or father vs. son) actually fought? This should be the less common and more historical occurrence, and so should be the easier answer to produce.

Then, setting those few cases aside, what I'm wondering is what happens when one active champion has a brother, father, or son move up the rankings of a particular organization and finding themselves cast by circumstance into the role of mandatory? Has anybody ever been stripped of a title for refusing to fight their brother/father/son?

Are the rules of the governing bodies regarding stripping a titlist for refusal to face a mandatory challenger hard, fast and fair or do they have provisional discretionary wiggle room to say "No, you don't have to beat up your dad on pain of having your dreams snatched away"?

If this hasn't ever become an issue, I would imagine that it inevitably will, as boxing is every bit as much a family affair as any other sport, if not more so.

For instance, say Jose Miguel Coto goes on a nice streak and shoots up the WBO rankings and before you know it, is sitting at #1, with Miguel Angel still the champion. If one or more of them was unwilling to take this fight, would it be at the expense of ranking - or even title?

You also have both Camachos campaigning at 154 - and while neither is really seriously contending right now, Jr. is fighting Yori Boy Campas right on his father's heels. Certainly with a couple of quality wins in a row each they could find themselves as eliminator candidates...

And of course, there's the much-discussed Klitschko unification. Say one brother was willing to get it on and the other declined...would the latter's HW title claims be forfeit?