Cracked Cast Iron Stack or junction between toilet and shower

Our house was built in 1937. Sometimes when this particular shower is in use, it leaks heavily into a closet on the 1st floor. Sometimes when the toilet is flushed, same thing. There is a tile floor in the bathroom. Does it sound like we need to rip up the floor to figure out what is going on? We just finished remodeling it... There's about 5 feet between the toilet drain and the shower drain. Thanks for your help.

Or you could open the ceiling in the closet to see what is leaking.

You remodeled it without checking the piping, or did you not redo the floor during the remodel? you can open the ceiling under the leak to see what is happening, (or make a small hole and have a plumber look inside with a small inspection video camera), but in many cases, you will have to break the floor in the bathroom to actually do the repair.

Did not redo the floor during the remodel as the tiles are in great shape. Will try to check it out from below first, and maybe with some luck we won't have to tear up the floor. Teen girl wants her new bathroom back! O the pressure .