OK so obviously they didn't nurture you well and our parents are not our responsibilty. You owe them nothing and it's not your job to force them to be healthy. Nor will they listen to you. Continue to call once a month and live your life for you...as for your brother...tell him you plan to call once a month and he could do the same two weeks apart from you so one of you are checking in every two weeks.
As for illness and health insurance...I have no idea where your mother is but in the USA they have medicaid for people with no insurance and county hospitals treat everyone with or without insurance.
Good luck to you and again it's your life, live it to be happy.
"Farts like a butterfly, stings like a bee"
REAL food rocks!!
Weight loss is only a side effect of good health!