Widening the stone entrance into a crawlspace
Widening this opening to any width less than a foot shouldn't be any issue. Even if there's a bearing wall resting above the bottom plate from the story above, it looks like the bottom plate matches the floor joist sizes and it will have plenty of capacity for spanning such a short opening. Just make sure you notch the opening as vertically as possible and the base of the cut into the wall is not cut back more than the top.