This is what we did:
Travelled up to where fc lived on the Saturday (2-3 hours from home), stayed first night at my brother's place, which is luckily only 30 minutes from where fc lived. Next day into a holiday let (paid for by ss), leaving dd1 behind with my brother.
Monday we went and waited on fc doorstep while she moseyed back late from 'our last holiday together' . Met dd2. Felt overwhelmed. Monday night brother brought dd1 back to stay with us.
Tuesday dd1 came with us to meet dd2. Tense day in fc house - fc disliked dd1 on sight, muttered audibly about her being a little madam, wouldn't let her play with any of the many toys in the house (dd1 was 4). It felt very awkward trying to keep dd2 entertained/protected from highly hostile atmosphere, while focusing on dd1 and trying to learn as much as possible from unmotivated fc.
Wednesday dd1 came with us to spend day with dd2. More of the same. dd1 behaving like an angel but was still treated very poorly by fc. I decided this wasn't fair on her, and asked my db to come and collect her the next day. Our sw fully supported us in this (she was incandescent).
Thursday went into town to meet birth mother (against wishes of fc). dd1 entertained by very nice sw until my brother turned up to fetch her. Birth mother didn't turn up; sw rang her and rearranged for next day. We went back to fc in the afternoon - big row as she felt we shouldn't be meeting with bm and how dare we fix another meeting with her when she had told us not to.
Friday we had review meeting, then back to fc for the rest of the day. Tense.
Saturday we went to say goodbye, then back to my brother to pick up dd1, then got home by 8pm. Front door lock broken; didn't get in the house till 10.30pm.
Sunday 10am fc arrives with dd2 and, finally, exhausted, we can get started.
So, in theory first meeting without your bc, then bc gradually introduced and spends longer with ac each day. The idea is very much that introductions is for all the family.
So why have I shared the awfulness of our experience? Because I think you need to be aware that it can be very tricky managing everybody in this situation. Most fc don't kick off like ours did, but it is an emotionally exhausting experience and not helped by having to take care of the competing needs of two children. We were lucky that our dd1 was very positive about the adoption and behaved really well. Also lucky that dd2 was only a baby, but fascinated by dd1. I'm really glad that my brother lived nearby and we had that back-up. Also that our social worker was very fond of dd1 and really wanted to make the experience good for her (she gave her a congratulations card with a medal saying 'world's best sister', which was a lovely gesture).
Hey, it's like childbirth. It doesn't last for ever