Not what you want to hear, but:

The spider plant might make it down to about 35F, but the pothos and croton are goners if it gets below about 50-60F. And I'm not promising anything about the spider plant. You haven't said what sorts of temperatures you expect to see during the winter, but the line not to cross is right about at 55F, so make your best guess.

If you experience temperatures that fall below freezing, the plants would surely freeze solid in the cement container. If you don't wish to move the pot, then how about transplanting to another container that you can move...to a protected area such as garage where it can be given added insulation.
Otherwise, remove the plants, pot them up and bury pot and all into the garden in a protected area such as amongst the foundation plants, up against the wall of the house.
Water them as required.

Ideally, such plants should come indoors for the winter.
The problem of having 3 plants in the same container is that they should have the same needs, fertilizer, watering, sunlight requirements. If not, then each plant may have problems and transfer such to its neighbor.

Cement I would guess is a good conductor of cold and as such would cause freezing of any moisture in the soil readily. I think you have to consider getting the plants out of that environment.

Pothos (Epipremnum aureum) and Croton (Codiaeum species) are only reliably hardy to zone 10. Spider Plant (Chlorophytum comosum) is apparently root-hardy to zone 8b (will die back to the roots and return in spring).

There is no way that the first two would survive with their pots buried in the garden, even in a protected spot, in USDA zone 7, which does experience freezing winter temps. There is a possibility that the spider plant might survive such treatment, but I wouldn't do it to any plant of mine.