As Anke says depends if registered parents ,with the british breeds some outcross to different british breed to improve a trait and I think 3 female generations they are back to say BA. If you milk record / show the mothers that will add prestige to your goat family. If unregistered you can register them on the identification register but it takes more generations to grade up to a breed. If they are quality goats they will do well regardless of registration.
Also worth checking health status are they from a cae negative herd.
I would say females you would be able to sell, even if unregestered, particularly if qualtiy stock you have to see what they look like, but unregistered males are worthless - meat / pets(castrate)/cull. Even registered males are difficult to sell even with excellent breeding /show results.
Off the top of my head current registered stud males in Aberdeenshire are: British Saanen, British Alpine, British toggenburg, Pure toggenburg, Boer and pygmy. Depends what route you want to do.
There are some breeders in Aberdeenshire who use boer and kids go for meat. (As far as I know only granton on spey and dingwall slaughter goats so it's a fare trek and then to butcher and home to your freezer.The breeders that sell their goat meat do not take other folks kids as they I suppose quite rightly, market their own stock only )