You are probably one of many people inquiring about this sibling group, and they need the video to compare prospective families.
I agree, I would do the video. It may be part of the "weeding out" process (I mean, if you don't want to do the video, perhaps you're not as serious as you think you are...is what it might put in the caseworker's head)
Even with sibling groups, if there aren't many "noted" problems with the children, then they are in high demand.
Please consider, however, no matter how "normal" they are, they could very well need professional counseling and transition time because of the life altering event of adoption.
I would gather your family and friends...anyone who is going to be in the family and social circle...I would have friends and family share why they want you all to have the kids and how great of parents you would be, and then you and your partner should each explain why you want a child(ren).
Best of luck to you
Kristi