Morton is right…You need a plumber. But if your husband feels confident (he removed the toilet, so he must know something…), he may be able to fix this.
What you have is a blockage in the drain pipe from the toilet. Clearly your tub (and, it seems, your sink) drains into the toilet waste pipe, and the blockage is downstream from where the tub and sink connect to the toilet waste pipe (that will be the 3″ or 4″ waste pipe).
Your husband might try running a snake through the closet bend (the hole in the floor where the toilet is connected). That should clear the blockage. Since you already removed the toilet, snaking out the line should be easy…if you have the snake. If not, do as Morton says and hire a plumber.
NtP