Kshyatriya (chhetri) is not a race. Caste does not equate race. Both, the brahmins and chhetris were indo-aryan immigrants to the nepal region. Because the chhetris are supposed to be political/warrior people, they mixed with the Nepalese mongols who inhabited the region. Which is why the chhetris of nepal look mongoloid today. With the shah and rana family, they wanted to preserve their indo-aryan qualities so if you notice, they usually marry into their own family. Unfortunately, not only do they look mongol (as in their efforts are useless now), but the inbreeding has caused massive mental problems in their entire clan. The Kshyatrias of India (who have not mixed with the mongols) and therefore look Indo-aryan, will not accept the nepali chhetris as true chhetris. As for Nepalese Brahmins, some have managed to be relatively 'pure' and some, I suspect did mix with the mongols at some point because there are some brahmins who look phenotypically mixed. It's a damned if you do, damned if you don't thing: for example, if you're pure, that means you're inbred and very impure, if you're a mongol mix, you're not pure indo-aryan and therefore impure. This is probably you won't see many brahmins looking up their family history. They're afraid of being either a mongol mix or inbred.