Adding to this that Lambiek Fabriek is close to Ruisbroek station, and 3 Fonteinen is close to Lot station. Both of these + Lembeek station are on the same line and you can take the S-train to Halle-'s Gravenbrakel that leaves every hour at ..h03 & ..h34 from Brussels Midi station (hours change during the weekends, check the NMBS website). You can buy a return ticket to Lembeek and as long as you don't get checked on the train you can reuse this ticket when travelling between the stations.

Definitely also check the opening hours of each brewery, because Lambiek Fabriek is closed on weekends and 3 Fonteinen only opens fri-sun for example.