Dont worry sis..Reach out to Allah swt in prayer at night and do what you can to comfort your parents inshAllah. Stay strong yourself and keep smiling even through your harships. Last night I was reflecting on how the prophet (saw) must have coped with the burden of bringing the deen to his ummah. When we worry about the guidance of our brothers and sisters, he had the worries of our entire ummah. When this causes us sleepless nights, how he must have spent his nights I cannot even begin to comprehend. And from the descriptions, He (saw) would smile each time he entered his home no matter what he faced from his people. SubhanAllah, surely he was the greatest example of a human.
Just pray for your brothers inshAllah that Allah swt will soften their hearts towards their duty to the parents. Its not in your hands so if they know they are hurting your parents then they are answerable to that.