I'm inclined to agree with V here and say I'd take the tickets but make it clear that you're doing it for the kids and that you aren't comfortable with him coming as he made it clear you aren't family anymore. But you have to decide where that boundary is for you. What you're comfortable with.
M:26 H:32 T:8yrs ILYBNILWY/ "I'm not happy": 2/6/16 D-Day-discovered PA/EA: 2/10/16 Separated: 2/14/16 He's living with OW I moved to different state: 06/16 Currently: Trying to move forward