Listen if you married cadaan girl and your son married cadaan girl your grandchild will have your last name and lineage !Ye he would if he also was culturally Somali, he would look very ODD however. Same way you can see ''Ethnic' somalis from big tribes who look completly madow however since they carry the name of that qabiil they are claimed. But yh if he is not culturally Somali no.
They are still somali. It is up to you how you enforce your Somalinimo on them that’s why we need a peaceful somali Ethnostate so our Ethnic somali offspring’s can learn their culture & heritage.