The ironforge ballast rule has nothing to do with multibots... each ironforge bot is allowed up to 4 ballasts to balance the bot and not make it go too fast/be too light/be unstable due to high power motors.
You are already nerfing your bot by adding ballasts, so ballast weight is not actually active weight. Hence there's no point in "balancing" it with multibot weight by saying ballast weight must be shared between multibots.
tl;dr ballasts aren't actually making your bot better, so they are not relevant to multibot weight balance.
MW's can have four ballasts and HW's can have four ballasts, hence MW multibots can have four ballasts as well.
