There is a long case history involving these ordinances, including extensive documentary evidence that occupancy caps and definitions of "immediate family" were designed specifically to exclude blacks (in the first half of the 20th century) and latinos as well (in the second), taking advantage of both the fact that black and latino households are far more likely to include grandparents, aunts, and uncles, and also the (obvious, in retrospect) fact that municipalities simply don't enforce these regulations against white households --- again, a fact documented in the case history.
At any rate, the dispute upthread suggested that there was no racial justice aspect to the "Western-prescribed nuclear family", and whether you agree with the courts or not, there clearly is such an aspect; the allegation that BLM is exceeding its charter by railing against "nuclear families" is easily refuted, and we should have all known better than to raise this objection in the first place.