I found a transcript of the interview with Perla and this is what he said (which led me to believe the adoptive parents have a lawyer):
KGET.com exclusive: Interview with the California City police chief on Orrin and Orson West disappearance | KGET 17
Q: Are the members of the birth family cooperating as well?
A: Uhh they- yes. Yes.
Q: And have they retained a lawyer?
A: Not to my knowledge.
Q: And when was the last time you spoke with them or or interviewed them?
A: Personally, the last time I spoke with the biological mother, it was a conference call the day after the boys went missing.
Q: Ok so its been quite a while since you last spoke with a biological mother?
A: I personally, yes. Other people have been in contact with her, but I have not.
Q: Has anyone been instructed not to speak to the media? Like the adoptive parents biological parents....
A: Not by us. Maybe by their attorneys, but not by us.