Siblings: Siblings should not be raised to be caregivers.
Sibling Doesn't Mean Caregiver or Guardian.
As parents, we expect siblings to look after each other - "you are your brother's keeper" has been around a very long time for a reason, but there is a difference between a sibling and a caregiver. Parents assuming a sibling will take full responsibility for their brother or sister after they are gone are doing everyone an injustice. Please note that "looking after" or "looking in on," is very different than "having physical custody of." There must be a balance between the child with special needs and the needs of the sibling to dream their own dreams and have their own life, even if that life means he or she is unable to care for your child with ASD. It's great if your children can grow up having a loving, supporting relationship and wanting to help when needed but to raise your non-ASD child to know they are going to have to become de facto parent builds resentment between the children and against the parents, and isn't fair to anyone involved.
For single parents especially, sometimes there is no respite care available so siblings may have to serve as babysitters to fill in the gaps between school and work hours or even just a break to go to the store. Consider paying your child if he or she is used to babysit. Even if you can't afford to pay with money, pay with extra opportunities for their favorite activities, letting them pick the week's movie rental, have a later bedtime, their favorite pint of ice cream all to themselves, or even a reprieve from a chore may help grease the wheels and show your appreciation.