Adding part to the sides of an object don't appear when sliced

I have built a small window for a project for my son. On either side there are two “teeth” on either side and when I slice, the two parts do not slice. Is there something that I can do to fix it?
3WindowHolder.skp (114.1 KB)

There are internal faces under those wedges. Delete them.

There are internal faces under the bevels, too. They need to be removed.

Compare this one to yours.
3WindowHolder solid.skp (114.1 KB)

Thank you. I completely forgot about that