Yes, it is possible to obtain subsidised treatment at IMH for Singapore citizens. IMH is a restructured hospital. One easy way to find out the details of the subsidy is to look for information on the IMH website.
Then look under 'clinical services', then look for the heading 'charges and schemes'. The charges for outpatient and inpatient treatments are listed on the IMH website. I do hope that you will take the important step of seeking help for yourself and your loved ones. There is no health without mental health. Wishing you and your loved ones a speedy recovery!