उसका is 'his', 'her' or 'its'. उसके is the form of उसका to be used when it is followed by a masculine plural noun.

उनका is 'their' but can also be 'his' or 'her' if you are being respectful/formal to/about whoever you are talking about. उनके is the form of उनका to be used when it is followed by a masculine plural noun.