Ellen
PIP is not an issue as it is not affected by any income you have, however, for ESA you can only earn money under the Permitted Work scheme, there's a guide in the ESA section. PW sets limits in hours and earnings, currently, you cannot work for 16 or more hours a week and can earn no more than £125.50 after deductions.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems