Teachers should not work on their non-contracted days. However, they must work the prorated directed hours on their working days.

Depending when meetings fall, you may have to allow them to not attend certain days if this takes them over their directed hours or pay OT (usually at single time). If meetings fall outside their working days, thus, they work less than their directed hours, you should create an individualised directed time schedule for their working days. Some teachers may agree to attend parents evening on their non-working days to make up the time but I would get that in writing from them year on year and build that into their schedule.

With leadership, there is an expectation that they work above directed time, but you should always have a directed time schedule to work from.

Do you have a directed time calculator that you use? Various unions have them (NEU Directed Time Calculator, for example), or your school/college may have its own version. It's a convenient tool for working out fractional FTE staff for the directed time of tasks/activities outside of classroom teaching. For example, within our College, I can use the calculator (it's actually an Excel formula) to see that a staff member on FTE 0.6 needs to attend 12 hours worth of parent evening events out of 20 hours for a 1FTE staff member.