You see the higher price for K class because there is only 1 seat available in J class.

You can buy the J class ticket for 1 person, but most likely you will have to buy K class for the 2nd ticket, because J class is no longer available after you take the 1 J class seat left.

Or you buy 1 J class ticket now and wait for J class to become available again, and then you buy the second J class ticket. There is no guarantee that J class will be available, but it is worth a try.