Well your father's close relative could have quite a radically different ethnicity from your father. For purposes of ethnicity only a test on the person of interest has any meaning. Even brothers and sisters have shown major differences in ethnicity due to the random recombination that is normal with DNA.

23andMe and Ancestry and FTDNA and GEDMATCH all use different sample populations. Most people get a different result at each and every service. People who have used all four admixture services have remarked that no two of them give the same results for them

Remember that there was so much migration around Europe throughout the ages that being able to attempt to break it down further than European is a very difficult task and it may never be able to refine them adequately. With the different reference populations they use, what one classifies as a Great Britain marker may be classified by another as a German or Scandinavian marker.

I'm actually unusual in that I am one of the few people who gets consistent results at Ancestry, FTDNA and GEDMATCH. I haven't done 23andMe.

For people of European ancestry, I doubt that it will ever be possible to get consistent results from service to service.