Cennétig mac Lorcáin, King of the Dal Gcais - The cennetig tuatha as a kindred group, most have had other smaller tuath

I am writing to find out if anyone ells has thought that the Tuatha of the Dal Cassan, most have had other smaller, Tuath with them when they made their exodus from the Northern Desise mumu. If so who,? as it's hard to see so many related kindred coming from just one line of family members,? not impossible but unlikely , as we know inbreeding on such a scale, would lead to deformities and a fall off in population. So wives most have been brought in from other outside Tuath, so as to keep the Day Cass growing, and spreeding out over their territory. To do this they would have had to be able to defend as well as attack . This most have taken more than just one or two generations to achieve more like five or six,? My email is lobobehan@gmail.com please excuse my spelling as I'm dyslexic, but am an avid Historiean. Please answer any of my question as I have lots of work done on this subject over the years.