It sounds as though you have what is called “salmon” brick. These are soft, pinkish-orange, brick that were fired at too low a temperature to be used in exposed locations. In the kiln, they were usually located at the interior of the stack and did not receive the heat that the outer brick got. In the 1800’s, masonry walls were load bearing and were very thick (12″ or more). The salmon bricks were used as a filler between the outer wythes (layers). If these brick are ever exposed they crumble to dust. As far as I know there is no repair other than to cover them with a layer of hard fired brick. Salmon brick are no longer made. Todays brick are consistantly hard fired. A local brick mason may have other repair suggestions.

Regards