oj, Am so glad that Steve is still with you all.
Happy birthday to your girls - I hope they have a lovely day.
Wrt Steve's family, it's hard to imagine that there are such bitter and twisted nasty people out there who can behave like this at such an emotional time in all of your lives. One can only hope that a lot of it has to do with their own sense of loss, and regret over the past.
As for Mike, is it possible he thinks he is doing good? that he has traced your family because he wants this to look like some kind of gesture from Steve? How much does he know about your birth family and about the circumstances of your growing up in the care system? If he doesn't know the details, and that you wouldn't actually have wanted contact with your birth family, then this may just be a misguided attempt from him to do good, to try to put you back in touch with some family at a time when you are losing Steve and family is important, iyswim?
From your posts about Mike in the past he does sound like a reasonable person on his own, and not the type to maliciously try to put you or your family in danger.
Obviously I could be wrong, and if he is aware that you wouldn't want contact with your family then you should speak to SS asap and voice your concerns. They will know how to proceed from here.
I am out all day today but I will be thinking of you all. xx