Any sudden death (other than from a fall or other physical injury) should be investigated by a qualified reptile vet. They can do a necropsy on the body (providing it was refrigerated after death, not frozen). This is the only way to find out why something died after the fact.
As your second male is showing the same symptons and you waited till the third day to seek help, may not be anything we can do to suggest to save him, other than take him Immediately to a vet. (even then, depending on the cause, this may not save him) IF he doesn't make it, refrigerate him (after death only) and bring him in to a vet for a necropsy.
To even give a guess on what happened to your first male and is apparently happening to your second male, we need to know details about how you have been keeping them for the last several months.
What size cage are each in? UVB light, Basking Temps? How often you feed? Are you supplimenting with calcium powder/vitamins? Are they all housed individually or were they all in one big cage? Have there been any changes to their care/environment in the last week? (since the first male started to get sick)? Now this doesn't mean just within the cage but in the house itself (any renovations in the house? If in an apartment or duplex type set up, have neighbors sprayed for bugs? (ie roach bombed their apartment?)
Again I recommend taking your male and at least one female in to a vet (separate carrying cages for them, boxes or rubbermaid containers are fine, as long as they are big enough for your dragon to lie in comfortable, without their tail bent sharply). Parasites are not likely to cause dragons to go downhill fast. Toxins, viruses etc, are more likely to cause this. Or extreme temperatures.
-----
PHLdyPayne