Kittens need to stay with their mother and litter mates until at least 10 weeks, TEN WEEKS, and twelve weeks is better. They learn important socializing behaviors in those extra four weeks. Bite inhibition for example.
In your situation you should take two kittens so they have each other for company. At 10 weeks. No sooner.
Your neighbor should take that pregnant cat to the vet and have her spayed. He is extremely irresponsible for not doing it already. This world already has too many unwanted kittens and cats because of people like him. Sick and dying and suffering.
The kittens from that poor cat could already be in poor health, inbred, who knows what the mother has been fed, with no vaccines, no vet care, you are setting yourself up for disaster.