I wouldn't consult S15, I would just go ahead and make plans with him. And with your dad if he is still alive. Father's day is about fathers, and you are not her father. I would leave her out of plans and then if she contacts you about it you already have plans.

Enjoy the day with your awesome S15! (P.S. I wish I had such a good relationship with my D14......)

M(53), W(54),D(19)
M-23, T-25 Bomb Drop - Dec.23, 2017
Ring and Piecing since March 2018