Você precisa usar duas junções para fazer isso.
Por exemplo:
select f.friendsID,
s1.name as personA_name,
s2.name as personB_name
from friends f
inner join student s1 on s1.sID = f.personA
inner join student s2 on s2.sID = f.personB
select f.friendsID,
s1.name as personA_name,
s2.name as personB_name
from friends f
inner join student s1 on s1.sID = f.personA
inner join student s2 on s2.sID = f.personB
