I think that being on a list requires registration in a district, so that, yes, there are only three districts where both the Flemish and Walloon parties are on the ballot. Ideologically aligned parties across language groups don't automatically form coalitions. There's quite some politics involved. But I think that practically, they will still end up doing so.

There is a small German-speaking community, but it is too small to field its own political party for the elections. It does have a separate senator in the senate, otherwise it votes in the Walloon district in which it lives. As Belgium is a federal state, the German community also has a large degree of self-governance.

The poll in Brussels was only with regard to the French-speaking parties. I just found another poll of the Dutch-speaking parties, but that one is already over two weeks ago.

Why Verhofstadt has not been able to govern effectively is stuff for another diary.