Wherever you read about "arrondissements" (which don't exist here) and parts of Brussels being French or Dutch, sorry but Brussels region is officially bilingual French AND Dutch. However, in the Belgian population, only 7% of inhabitants out of 1.1 million speak Dutch as 1st language, 93% of Belgians put down on their registrations that French is 1st language (for many of those it could in effect be a 2nd language, Arabic, Turkish etc first). There are 19 municipalities in Brussels region, the ones with most number of Dutch speakers are in the north-west eg Berchem-St-Agathe and Ganshoren.
All Flanders is officially Dutch speaking, Tervuren being a municipality in Vlaams Brabant, one of 5 provinces which make up Flanders. Tervuren has only about 70% Dutch speakers, there are so many English speakers there and French too. west of Tervuren is Wezembeek-Oppem, also in Vlaams Brabant but with "facilités" for the in reality 80% of French speakers! Wezembeek-Oppem on the border is actually less than 1km from the gates of BSB - Rue de la Limite! Then you have also in Vlaams Brabant the municipality of Kraainem with "facilités" for the 80% French speakers. Then you have in Brussels region Woluwe-St-Pierre which has a Belgian population of 92% French and 8% Dutch, but in fact the international population is close on 35% now.
For Wezembeek-Oppem and Kraainem French schools (4 of them), you must live in one of these municipalities. For Brussels region French schools, you can live anywhere.
Maternelle is 4 years here, in September 2013 it is children born 2011, 2010, 2009 and 2008. Primaire is 6 years here, in September 2013 it is children born 2006 to 2002. Most schools have maternelle and primaire together, but a few are separated into 2 schools and not always right next to each other. You are rather late to be looking for French school places. You will need to phone all the schools, maybe several times too. You will need yo be ready with their year of birth and school year you are looking for.
A BSB full time teaching salary, with no housing allowance, should allow you enough income to afford a 3house costing 1.5k per month, you could get a 2 bed for less or a 3 bed apartment. You can get a 3 bed house for that price. There are no cheap French majority areas near to BSB. The nearest cheaper areas are in Vlaams Brabant, such as Leefdaal, Dutch speaking, you'll end up spending much time in the car, which added to the cost of rent might end up the same as living in an area with majority French speakers. You can easily live without a car in Wezembeek-Oppem, Kraainem and Woluwe-St-Pierre (WSP), the 44 tram and 315/317/410 buses go to BSB from these areas, very cheap and BSB will give you a tiny public transport allowance which will cover some of the cost of public transport.
So what job at BSB has your husband got? There are a few mumsnetters connected with the school.
Look at the following school maps. The Brabant school map includes the 4 French schools in Kraainem and Wezembeek-Oppem.
batchgeo.com/map/1f1bf2b3b6e4ad41fe67c1a57d56a826
batchgeo.com/map/cede6049273e541514fd4c1c5dc4af9b