I’m not sure, although (in NSW) the only restrictions on the intent of a Special By-Law relates to it not being in conflict with a “superior law” of the State or Commonwealth, not restricting any “dealing” to do with a Lot (e.g. a sale, lease), not restricting the keeping of guide/hearing assistance animals on a Lot, and not restricting the numbers of people under 18 years who may reside in a Lot.
So if the residents are over 18 years, an O/C may get away with the placing of some limitations on adult occupancy rates, but let’s see what our original poster was trying to achieve and where they’re located.