بسم الله الرحمن الرحيم
(1) Yes, she may wear, but it should be gold or silver ring, not made of any other material. (Fatawa Rashidia, p.595, p. 601, pub. Darul Ishaat)
(2) Yes, she may wear it.
(3) He may wear silver ring weighing 4 gram and 374 milligram. It is not lawful for males to wear silver or ring more than it.
Allah knows Best!
Darul Uloom Deoband