Is there any law about 5(3children) ppl living in a 1 bdrm apt?

I was wondering is there any law about living in a one bedroom apt with 5 people? My boyfriends ex has their 3 children (13, 12, and 7) living in a one bedrrom apt with her and her 25 year old boyfriend. We both find this to be wrong especially since the daughter is the one thats 13, having no privacy around a 25 year old dude. But is there anything he can really do about it? The mother told the daughter not to tell us but she did and I have confirmed through research that it is definitely a 1 bedroom under 700 sq ft. They arent living there because they are destitute but because the ex just doesnt want to shell out money for something bigger. So what can be done if anything? Its in the state of Missouri if that matters..