Earthmother - you are a wonderful foster carer. Am retired after 30 year soc work career in child protection, fostering and adoption. Have taken many newly approved adoptors to see their child for the first time in the foster home, and the way you handled things was just perfect.
Sadly I have seen foster carers who have not even asked the adoptors if they'd like to hold the baby and I have had to say "I think x and x would like to have a little hold" and the carer has handed him over, and then the adoptors are dead nervous as you say and much more so if they think the carers are monitoring them. I have had to use all sorts of tactics, like saying to the carer "Would you mind if we asked for a cup of coffee" just so the adoptors could have a few minutes with their baby. I had one carer who would not hand the baby over, saying he had his injection yesterday so he would cry if anyone else held him and "anyway it's time for his sleep" and the adoptors are too nervous to say anything.
I had a few strong words with the foster carer who refused to let them hold the baby and she was better the next time. I have to say that these kind of foster carers are in the minority, but it does happen, especially if they don't like something about the adoptors.
Needless to say it is so much better if the foster carer can be like you earthmother, and the adoptors feel they can phone for advice about the baby's routine etc, especially if they are first time parents.
Social workers are never there on hand-over day but we do make arrangements about the way it is to be done and timing etc so that everyone is in agreement and mostly the hand-overs went well. Had many traumatised foster carers on the phone though over the loss of the LO. I always advised that talking to foster carers who had done it a few times would be best as they would understand more how they were feeling.
Good luck to all concerned.