I have a friend who had a very irresponsible cat owner in her street. She used to grab the cats when she saw them and nobody was looking and turn them in to the local cat rescue. Not that I'm suggesting you do the same or anything.
Oh I know! Those bloody cats have no common sense and the moral of ...well, alley cats!
But I don't know what you can do TBH. The owners are very irresponsible and lazy but I don't know what to suggest. I know people on here don't always rate the RSPCA but perhaps a call to them for advice to start with?
Cat Protection League in my area do a voucher scheme where it costs £5 to have a cat neutered/spayed. Might be worth looking into that in your area. Though if she is that stupid, I would second the rounding them up and taking them to the shelter approach as if she can't afford to neuter them they'll not be chipped either
RSPCA will do nothing, they are useless. Cats Protection may help and will certainly advise. Otherwise call the environmental health/police/SS - her child should not be living in such conditions even if she chooses to.
definitely get in touch with the rescues in your area and hate saying this but yes the rspca aswell, my daughters neighbour was like this woman, she got in touch with cats protection and what they did was arranged a day to pick up the cats, my daughter lured them into her house while he was out, the cats protection picked them up and to this day the neighbour does not know where his cats vanished to, sounds sneaky and not nice on him, but the mom cat had five litters one after another, by the fifth the kits were coming out dead or deformed and it was for the cats good, she is now living somewhere where she is cared about, and so are the two daughters he kept, all of us did the pleas to hm to get the cats spayed but no way was he going to so drastic measures were needed
i think the fact theres cat shit all over the house will be grounds alone for the rspca going in they have more powers to remove animals now even if they only remove the mom and kits at least thats 8 cats that will get spayed rehomed and have a better life, what they will probably do is advise her to get the two daughters spayed and if she dosent they will probably remove them at a later date
also if the rspaca dont do anything and you have to go the rescue center and snatch route get them on the waiting list first as all rescues have long waiting lists now and it wont be a case of snatch cat take to rescue you would have to time the snatch to them having a free place and inform the rescue center what you would be doing, also if there loads of cats in a house they dont get the attention they should and if not handled early enough become lifelong cats that are not human friendly so if they go to a center are harder to rehome because everyone wants an approachble cat ideally, sorry on me soap box, i work at a rescue center so see all sides of cat life
linerunner our vet will spay kittens from ten weeks or 2kgs wheight and a lot of vets are coming round to this way of thinking get em before they turn into potential moms and dads what they aint had they dont miss