You are contradicting yourself here. The shared ancestry between groups like Beja and Somalis is very ancient, none of these groups share recent ancestry with Somalis (with the exception of certain Oromos). If it weren't for the Cushitic language family most wouldn't even be up there. It's definitely language what is the most important factor here. I am done talking about the Rendille genetics. The Tishkoff study did not find any significant non-Northeast African admixture in them - fact , you can misconstrue her words all you want but that doesn't change this simple fact. Ethnic kinship is not determined by admixture but through language and culture. 

 I'm going to add the Rendille as a related ethnic group, I hope you respect my and Gyrofrog's opinion. You may alter their page to show their relationship with Nilo Saharans. I don't mind as this doesn't change the fact they are related to Somalis.