There are no restictions on Y IKK.

For International J:
1) if you are travelling on IKK J ticket, you can use IKK for J seats for anyone travelling with you, of course subject to seats being available .
2) if you are not flying, you can use IKK for J seats for immediately family members only.
3) if you have a purchased J ticket, you can use IKK for anyone, so long as they travel one of the international legs with you.