If a person applied for a green card from a certain visa type, but he had family members who have long term B1/B2 visa now staying outside US, Are they permitted to come, not questioned on the border? Because there’s another family member staying inside US applying for Green Card?
First of all, everybody gets questioned at the border.
A green card holder may petition for family members to immigrate, but this procedure is limited to immediate family (spouse or unmarried children). This kind of family member visa is limited in number per year. There will be a period of time to wait, possibly many years. See Visa Availability and Priority Dates.
The family members can come to the US in B-1 or B-2 status, as appropriate, but they will be subject to a normal interview like any other temporary visitor. In fact, they might have a harder time: the fact that they have a relative applying for a green card may make it more likely for the immigration officer to suspect immigrant intent on the part of the family member who is seeking entry. If the officer finds immigrant intent, the traveler will be unable to enter in B-1 or B-2 status.