Father in law put reddish gas in my mother in laws car ? Help?

My boyfriends dad put reddish brown gas in my boyfriends mom's car and now its acting funny it was in a car sitting in the drive way that didn't work he punctured a hole and took that gas out and put it in his wife's car and now its cutting out and its hard to start what could have happened we know its bad gas and the car he took it from was sitting there but he is 87 years old and didn't think about it till the next day and we have put new gas in it anything else we can buy or do to help her car ? And don't be rude with you answers thanks