Read my post again, specifically the part with Jill, when she says that she definitely wasn't playing against a beginner. Jill plays tennis regularly and the MC doesn't. The MC used to play tennis, so it's been a while since he played tennis. So if he hasn't played tennis for a while and Jill says that she's not playing against a beginner, the MC used to be very good at tennis and you won't be if you have to teach yourself everything. Ergo, the MC had tennis lessons that Neil couldn't afford.
I always forget, so I often assume, so that you remember everything. What did Neil say to the MC on his birthday? So that he and Lynette weren't married. Now a child is born and the mother dies during the birth. Who had the baby MC?
Someone who claims to be the father (not married) or the parents of the deceased woman, who could easily prove that they are family members of the baby MC. Of course you're thinking that this can be easily done with a paternity test, but it's not that simple. Why?
For a paternity test, you need blood samples from the father and the child. But because the grandparents had guardianship of baby MC, they can prevent genetic material from being taken from baby MC. Neil's legal battle. Neil probably fought for his son for years until chance helped and he got verifiable genetic samples for his son.