You don't really know what is happening in their lives so you don't have all the facts. It seems to me that the only place to get more information is with the in-the-middle friend.
You are however wearing different hats here. When you where taking the pictures at the wedding, you were the photographer. Now, you are the businessman. So you need to ask yourself, in the big picture of things, what is the best course to follow for your business? This would not only include money, but also goodwill, and your reputation too. No one can or will watch over those things for you.
If you are holding the pictures then you are as they say, holding the cards. You don't need to rush into anything at this point. The mistake was made by not getting the money up front. When clients try and come down hard on me for insisting for the money up front, I tell them it is necessary so nothing comes between us after the wedding, I don't want to feel like a bill collector and have you hide when I come around. When I see you I want an open friendly family feeling.
You don't have that feeling with them now. It is exactly why you want to get paid up front. If you turn into a bill collector, you no longer have that nice relationship - it leaves - totally. I think we all have to go thru one of these type of ordeals to have first hand experience why to collect up front. this one may be yours
But still, they may be having marital problems, or something else may be going on, or they may have spent all the "envelopes" they got at the reception (another reason to get paid BEFORE hand) already and no longer have any money. The pictures move downward on the priority list REAL quick when that happens.
Still, small claims court, in my opinion, is not the road to take. I think the best chances are to hope they get to wanting the pictures eventually and nothing is going wrong with them. Your leverage at this point is not great, and any action like court may tarnish your reputation in ways you can't foresee now. I would contact the intermediate friend in a way that you seem concerned about the couple. If you get any more info, good. If not, back off, you have the pictures and they don't. If they ever want them, there is only ONE place to get them - YOU
Peter