They are no doubt acting as a single alliance. Most importantly, I have a policy of minimising exposure of information to opponents whenever possible, a policy many of my allies also follow. Thus the CD does most communication outside of the alliance through our foriegn minister, while public nobles like myself head up pledge chains and make public announcements. The original charge was that because we had nobles in common pledge chains we were in fact a single alliance. This is a misunderstanding of why we put nobles in pledge chains and what constitutes an alliance as opposed to an arrangement of convienience.
Nobles are in pledge chains because any member of the pledge chain can 'GET' things from a garrison.
I won't belabor the many ways that this simplifies orders. However, just because I share a pledge chain with someone does not mean we are allies in the sense that I think of allies. Indeed, there are CD members whom I have been allied with since turn 1 who are not in any pledge chain with me. Conversely, there are people whom I do not consider allies who have been in a pledge chain with me for many turns. Since I consider pledge chains irrelevant to alliance, it is fair to ask what I do consider relevant.