I would contact the FDC office and ask for more numbers etc so you don't get left in the cold.

Our FDC carer often would "interveiw" in October/November the families and try to get everyone to "fit" best. So, she would try to space ages and personalities on the right days and try to get everything everyone wanted and it took her a while to get it all organised. If the carer has spaces for a few kids at once, she may find it easier to fill having the two children.... it seems unfair but I guess if they are able to pick & choose they will, ykwim?