Giving the past posts you have placed, the cause of your male dragon's death could have been many things. Stress from fighting, being caged with too many animals and not enough space, respiratory infection, improper heating etc.
My suggestion, Take all your animals to a qualified reptile vet for full examination, blood work, fecal exams, the works. Also, pick up the 'Bearded Dragon Manual', 'Your Bearded Dragon's Life' (by Liz Palika) and spend as much time as you can reading caresheets on the internet, including sites like www.beautifuldragons.com and www.bearded-dragon-network.com/oldbvd/?PHPSESSID=888e9a78a569d437f072e321e2db4101

