Diocletian's original given name was ÎÎ¹Î¿ÎºÎ»Î·Ï (Diocles), which is a very common Greek first name. The meaning of the name is uncertain, but Î´Î¹Î¿Î¹ÎºÎµÏ means to rule and the first part of the word (DIO) has the sense of a god or a lord. Your guess is not completely off base, however, because words for two are similar.
Pant sets are another fashionable approach to take when deciding how to wear pants for your mother of the bride/groom look. They come as a set and are often made of chiffon and silk material. The pants are generally flowy, which creates a more dressed up look.
Yes the parents should match the formality of the event. I would probably just tell the FOB and FOG that the GMs are wearing X and then let them decide what they want to wear from there. But in the end if the FOB wants to wear a pair of sweat pants and a t-shirt with holes there is really nothing you can do about it.