Docking Troubles

Hi all!

So, I was trying to dock the three ISS module made by Nododu1 (https://www.simplerockets.com/u/Nonodu1/Posts). I had no problem docking the first one, but when I try to dock the second one, the first two module disconnect themself when I approach them with the third. Is this a bug? Or is there anything i could have made wrong?

Oh and by the way, is there a way of making two docked element behave as a single one? When I want to activate Solar Pannel or RCS of docked parts, I need to take the control of the Command Pod of the two modules, one after another. And if two command pod aren't in the same direction, it's tricky to set a directionnal manoeuver. Oh, and Solar pannel only fill the battery of the module they are on. Not the docked one...