New FP needing some experience.

My wife and I are fostering 2 girls age 3 and 2. They are sisters who share the same mother but have different fathers. The window for mom's TPR is closing if she does not improve, so things looked like they could be heading towards a permanent placement with us. Just this week the paternal grandparents showed up out of the blue. They are requesting placement of their granddaughter. They live many states away so sibling visits would be very difficult. In your experience, have you had siblings split up to live with relatives?