Upgrading ad colligenda to full grant by attorney

Deceased died intestate about 10 years ago while in the middle of a divorce. The decree nisi had been issued but they had died before the decree absolute came through, so was still married.

Deceased’s sibling applied for and received a grant ad coll as attorney for parents (I believe under a general power, and one of them has since died). Not yet clear why spouse didn’t apply but there was some kind of dispute between spouse and the rest of the family. That dispute has now settled and a full grant is required to distribute the estate.

Would the sibling therefore apply as the current administrator or from scratch as attorney for the surviving parent, perhaps passing over spouse under s.116? Assuming that spouse didn’t renounce at the time of the ad coll application, presumably they would still need to be cleared off if sibling is not applying as the current administrator.