First of all, Suzanne's family was not anywhere near the area where Suzanne disappeared. Most of them hadn't even been in regular contact with her in the last two years. Secondly, Barry is the husband and was the last person to see her. So her family would not be held to the same standards as the spouse.
Third, they have already indicated that they did not want to reveal too much because they didn't want to hinder the investigation.
And fourth, since LE are treating the husband as a suspect it seems natural that he would be scrutinized more than the rest of the family.
In terms of searching, Suzanne's family did search the area when she first went missing. They wouldn't know where else to search without evidence that points to a specific location. Her body could be anywhere in Colorado.
Imo
Another big issue is that by publicly speaking they risk losing any relationship with Suzanne's daughters. BM does not. By speaking out, he can only bring attention to the case and possibly help find his wife, if, you know....
But everyone else is possibly between a rock and a hard place.
That being said, if I were family of Suzanne's, I think I would try to speak out, not about my concerns regarding who may be involved or about the investigation, but about Suzanne: Who she is. What she's like. Photos of her. Her life. Everything about her character. Her family. Her friendships. Etc. Just to keep her case in the public eye and maintain pressure, or create a sense of guilt in whoever might be involved or have info they're scared to divulge.