Thanks for some great tips!
I did some more research and was able to find some availability on MXP-BRU for several dates in May 2020.
However there appears to be a maximum of four seats I can book, and we are a family of five.
Does anyone know SN's policy for flights like this? Are there only 4 reward seats made available for each flight? Or can only 4 be booked at a time? (Meaning I would need to make two separate bookings.)