Did the counsellor say why he/she wants to involve others?
It really depends on the type of relationship you have with your sister and boyfriend, and how much involvement you want them to have in your recovery.
My mum has come to a couple of meetings with my T, and I found it beneficial. She found out things that I wasn't brave enough to say to her myself.
Ultimately, it's up to you. Do what you feel comfortable with. If your counsellor wants a meeting with them, do it in your time, and when you're ready. It doesn't have to happen right now.
I hope this has been helpful.
Good luck