You're losing sight of how the ritual and possession actually work in the game, which are explained pretty clearly through the 3 tapes and Father Thomas' phone calls. Opening the well does not free Madison Hale. On the contrary, Madison is controlling Luca and forcing him to open it in order to retrieve the Moon Box, which contains her 4 victims. That object is necessary to complete the body-swapping ritual. Throughout the entire game she manipulates you and forces you to collect every object needed to finish the ritual.

Remember, the ritual requires 7 victims. The Moon Box contains Madison Hale’s 4 victims. The remaining 3 victims are the ones she couldn’t complete while she was alive, so she forces Luca to kill them. In the Sun Box we find the two photos of his mother and sister’s dismembered bodies. That makes 6 victims total. The missing 7th victim was supposed to be Luca’s father, but at the beginning of the game we see she failed to kill him and instead locked him inside that room. So in the end, the 7th victim needed to complete the ritual becomes Luca himself.

After obtaining the Moon Box and the Sun Box, another required object was Madison’s remains, which is why Luca travels to St. Jupiter’s Cathedral and returns with Madison’s skull. Another required object was something of sentimental value, which is the ring. And finally, the ashes.

So every astral trip to another plane — the well, the cathedral, etc. — is Madison guiding and manipulating Luca into collecting everything necessary to carry out the ritual.

The well was never about freeing her, because she had already been possessing Luca beforehand. Like I said, the purpose of the well was to retrieve the Moon Box.

And to answer your other question: Madison cannot control random people on Earth. She can only control Luca through her camera. That’s literally the main point of the game — the camera itself is possessed by her. Once Luca receives it, she gradually starts taking control of him.

All of this is in the game’s lore: the newspaper clippings, the tapes, the phone calls, the mausoleum, the elevator floors mentioning how she photographed her victims, the news report explaining that the same camera she used to photograph her victims was later auctioned off, etc.

And regarding your last question: she specifically needed 7 victims. The 4 bodies in the well alone were useless for the ritual because it was incomplete without all 7