So can have three objects as part of your force. I thought it was one heavy, one light and the third was players choice. So this has come up in my group, can you take two Kryptonite?

Yes, as long as there is also a heavy. Kryptonite are light objects

Yes, all Kryptonite are light objects, which would mean your third would have to be a heavy.

Also you can not play 2 of the same Kryptonite on one team as all special objects are unique.