What will happen if a foster child makes a fake abuse claim against their foster parents?

My mother a step father have recently become certified foster parents. A couple of months ago they had their first two children come to stay with them; two sisters, ages 6 and 8. They were happy with the age range because I have a 7 year old daughter, whom they love and adore. (also I have a 3 year old daughter and a 9 month old son, besides the point, i just don't like leaving them out) So everything was going fine, the girls were happy (seemingly), and the six year old I even saw cuddling with my mom during the fireworks on Independence Day. Then suddenly someone came and picked the girls up stating that the 8 year old had made abuse allegations. I don't live with them, so I don't know if they were strict with her, or if she just has problems, but I know that my parents would not abuse any child ( I was way worse than any 8 year old could ever be). Now, as of yesterday night, they were sleeping in their beds at my parents house, and tonight both the girls are gone, my mother is sad and heartbroken, and i'm sure the six year old girl is sad and upset, even if the 8 year old wanted to leave. And they are doing and investigation, which is my question comes in. What will happen after the investigation is complete and they deem it unfounded? Would they bring the girls back to the house? If the six year old wanted to go back to live with my parents even if her sister didn't go, would they let her?