Lorraine
The means test for ESA(IR) takes into account yours and a partners income, but would not include your son.
However, other benefits enabled by ESA(IR), such as Housing Benefit, may assume a notional payment by your son to the household. You would need to speak to your local CAB or Welfare Rights office to understand any deductions made in these circumstances.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems