They are also in the Festival of Fantasy Parade. So, you can wave at them as they go by.
If you want to meet them, it is best to get a fastpass. Just know that you will meet both of them, but separately. You will see one, then the other.
If you have a longer trip, it shouldn't be hard to get a fastpass towards the end of your trip. We went in August for 16 days. I only wanted one FP+, on our second day at MK (day 9 of trip). I had a choice of any time I wanted that day.