It seems to me that if the government has the resources to take people’s kids away, then they ought to have the resources to provide adequate housing to reunite families.
But if they aren’t going to do that, then how about this?:
Require that foster care include housing of the rightful parent(s)/guardian(s) in cases where housing is the only obstacle to their lawful reunion.
If you are generous enough (and compensated?) to take in three siblings, how about you also take in their mother? Let them live together under your auspices. Help the mom to get back on her feet, too. Maybe you can even be an influence for good parenting and life-management skills. Foster mentorship might be a useful thing.
What we should not be doing is using the power of the state to break up families where the harm of the denial of the family experience is much more certain and severe than the relatively minor (and correctable) risk of future loss of housing or the seeming non-issue of needing to live in shared bedrooms. It worked for The Brady Bunch.