他人 is a neutral term for 'stranger' or 'unrelated person', while よそ様 is a polite, somewhat old-fashioned way to refer to people outside one's immediate circle.
よそ means 'another place' or 'outside one's home'; よそ様 adds the honorific 様 to refer politely to the people of that outside place.
Etymology
Combination of よそ (another place, outside) and the honorific suffix 様 (さま). The exact historical derivation is uncertain, but the word has been used as a polite way to refer to people outside one's own group.
