Like a PP stated, grapes can kill a dog!!
Your NF are truly horrible dog owners & my heart truly aches for this poor dog.
Since you have already spoken to them + they already know how you feel (and still haven’t remedied the situation), then it is time to issue them your walking papers.
This is your only option OP.
In the meantime, do not clean up any dog vomit and try not to step in it.
I concede.....
Easier said than done.
Especially if you are caring for a mobile child.
Too bad there is no agency like CPS - Canine Protective Services that you can call & report this awful family.
Sadly, they are killing their poor dog day by day.
