If PF had wanted to do that, it would be quicker to do a DNA test with his sibling. An Ancestry test would have to be taken by both people, just like a DNA test. If you,lindaromas, buy an ancestry test today and send it in you would receive results in about 3 weeks to 6 weeks depending on how busy they are. Mine took 8 weeks. It will give you a breakdown of your ethnicity, for instance it might say you are 28% French, 32% Japanese and some small amount of Russian. Then it will give you a list of people that are related to your DNA profile. It will start with those most closely related and then fan out. My daughter, who also took the test, came up as a sister/daughter or possible mother in relation to me. It shows generational DNA, but you have to establish the link. If a sibling took the test it would only show that they are siblings, but wouldn't determine if they had the same father. My daughter and her cousin who also took the test came up as possible siblings/1st cousins. We know they are first cousins, but the test itself isn't that accurate because it isn't testing against other knowns.
In contrast, a DNA test would test familial relations as well as unknowns, such as parentage. If PF wanted to know if he was a full sibling to other siblings an ancestry test wouldn't test for that, he'd need a traditional DNA test that would gather the maternal and paternal information for each sibling and then test the similarities of those matches. While Ancestry can show familial relations, it isn't decisive or accurate enough to determine if someone is your parent, sibling, grandmother, etc.
