Hope this works!!
Answer 1:
select p.name
from Person p, parent pr, parent pr1
where pr.childid = pr1.parentid
AND pr.parentid = p.pid
AND p.city = "kolkalta";
Answer 2:
Select ch.name
from (select pr.parentid,pr.childid, p.city
from parent pr, person p
where pr.parentid =...