Well, most likely you can't. Generally the cable is going to by physically seperate within the building back to the cable "node" outside between the different apartments. Cable company setup is going to prevent a MoCA signal from traveling between the apartments. There is a tiny, tiny chance that all of the apartments are actually sharing the same Coax, in which case MoCA would be a viable option.
I HAVE seen a few apartment building setups that were like that. However, they were generally "garden apartments" where you'd have, say, 4 apartments in a small building.
You'll need to use Wifi if you want to share an internet connection in this case.
As for health and safety, MoCA would actually be better than cable TV. It is transmitted at a higher frequency than Cable TV signals are on the wire, which leads to lower propogation/higher attenuation in the wire, as well as generally better shielding by the ground sheat of the cable. Now, the frequency difference isn't much, but if you want to be tin foil hat about it, you'd actually receive lower absorbed radiation from it than you would from Cable TV signals due to all of that (even though the 900-1000MHz of MoCA is slightly more readily absorbed by the body than the ~800MHz of Cable TV).
You'll receive significantly higher doses of electromagnetic radiation from cell phones, and not simply yours, but anyone within hundreds of feet of you, than you would from MoCA, running over Coax short of maybe holding the wire in your hand.
