Hi there UNOMAR it means your 7 year old cannot leave Prince Baudouin for another year, it's a strict rule, unless you're moving home you cannot change school between P1 and P2, P3 and P4. Your 2 other children can move school, but not the eldest.
Look most schools are good in WSL, why put your child in a school 2km away when you can put them in a school 200m away of the same standard? Divin Sauveur is just as near as Angélus - one used to be boys and one used to be girls so used to be twin schools.
Distance is ESSENTIAL if staying for secondary. For example, go against my advice and put your child in Don Bosco for primaire, instead of Angélus or Divin Sauveur, come secondaire application, your child will NOT get a place at Don Bosco secondaire, put them into Angélus or Divin Sauveur for primaire, you might get a place at Don Bosco for secondaire, but in fact you're more likely to get a place at excellent DDM next door to du Bonheur primaire, that is your nearest secondaire and one of the best regarded in Brussels. So the nearer your primaire, the better chance of a secondaire place at a decent one.
Given when you are applying, getting ONE school with 3 places is going to be rather difficult. I'd guess the only school you'll find that an easy task in your area is the school your children are already at as it's the least sought after in that area, though compared to schools in other areas of Brussels, it would be still quite desirable.