Should I tell on them?
Not reporting them does no one any good in a case like this. If they have a learning disability then they need to deal with that, and cheating isn't the proper way. If they don't really know the material then an employer will eventually catch on and they will be unemployed anyway. The PhD student has an ethical violation as do the people paid to do the homework.
If I were to beat up on you it would only be to suggest that they should have been referred to a professional when the learning issue became known.
But letting it go isn't a solution here.