Using merely a surname to determine a relationship between people is going to quickly lead your research to a dead end. Most genealogy is based on written records, and usually those are written by a third party such as a priest, census enumerator, doctor, or other official who are writing what they hear. Even ignoring these people hearing incorrectly or misspelling, a cursive 'r' and 's' can look very similar to people trying to read, transcribe, and index faded, smeared, and poorly scanned records. As an example, I am researching the Sproul family and have found the exact same person listed by the surnames Sproul, Sproule, Sprul, Sroule, Spooul, and even Groulx. Today there is one branch of the family that spells it Sproule, and one that spells it Sproul - but spelling does not mean they are not blood relatives. To establish or reject a relationship you must look at dates, places, and relationships as well - the sum of the information, not just select pieces.