Help needed

I have had 2 foster kid since dec. ages 6 and 7, last month I was told that adoption was what it looks like because both the mother and father wasn't doing their plan. So we had the option keep them if we wanted to adopt them or take their 2 year old sister and the girls for adoptions, or we could have the girls leave so the foster parents that had their sister could have them. So we told the social worker we could not take the baby but willing to take the 2 we had since they are 2nd cousins we want them to stay with the family. A week before the social worker had her month visit this month we was told we had to let our to go to the other house for a sleep over. When they got back they acted just fine but when the social worker came out social work told me they had a strong bond and had to be together so if we don't have plans on take ing the 2 year old they will have to place the girl together. After the visit the kids started acting like how they were when 1st moved in the 6 year started to have bad dreams and the 7 year old acting up and refuse to listen. Like the work told them something. I would like to know what I can do to stop the relocation of our 2.