Your son's earnings would make no difference to your PIP. Because you are on PIP the council should not make any non dependent deductions from your HB, so that won't be affected either.
His earnings won't affect your ESA, but if he lived with you (no matter whether he earned a fortune or nothing at all) then you would not be entitled to a Severe Disability Premium (SDP). Of course, you're not currently in receipt of that anyway, so this won't mean a reduction from what you currently get.
If it's tricky to call, send a short letter to the ESA people. State that you are now in receipt of PIP at the enhanced living allowance rate, that you live alone. Request that they consider your entitlement to an SDP. They may send you a form, Form IS10. It's a very short and simple one - complete it and return it to them. This is worth doing as, if entitled, the SDP is in the region of £60 per week. If you do move and live with your son, you would of course need to inform them of this and the SDP would stop.