You can make a caretaker agreement with your brother in law family and give it to society
Although still society can say that you must be receiving rent in cash even though no rent is mentioned in caretaker agreement
Parents are included in family members of society member. They cannot be called guest. So charging extra for parents considering them as guest is wrong
Record refusal of society to accept maintenance from you (without the above charges wrongly imposed on you)
Also write letter to district deputy registrar of co-operative societies for your ward and inform him about these pressure tactics of society and its secretary
You can pay the maintenance to deputy registrar if society doesn't accept or you can make money order in favour of society to show that you offered maintenance but society wrongly refused