Do your research. Do your background intel collection. Find out if your idea is even worth bringing up. Information is the first step in any endeavor, so make sure you have all of it.

Once you can manage that, you can determine the best way to approach.

Or, you could just accept that it's pretty awkward either way, in our society, to ask a married couple if you can get involved.

In the alternative, go out and find other people to crush on. Find the reasons you shouldn't like this couple, whether that means finding reasons you hate them or finding reasons that you don't want to step in to their lives in that way.

The best way to get rid of a crush is to find something to distract.