Given most people aren't reading the article, the particularly relevant points:

International humanitarian law lends hospitals special protections during war. But hospitals can lose their protections if combatants use them to hide fighters or store weapons, the International Committee of the Red Cross said. [...]

In an editorial published Friday in Britain’s The Guardian newspaper, International Criminal Court prosecutor Karim Khan issued a warning to combatants that the burden of proof is on them if they claim hospitals, schools or houses of worship have lost their protected status because they are being used for military purposes. And the bar for evidence is very high.

“If there is a doubt that a civilian object has lost its protective status, the attacker must assume that it is protected,” Khan wrote. “The burden of demonstrating that this protective status is lost rests with those who fire the gun, the missile, or the rocket in question.”

TL;DR: If Hamas is conducting military operations from hospitals, they can be legitimate targets in the eyes of international law, but precautions still need to be taken to avoid civilian casualties and the case for their military use should be overwhelming, not amorphous or tenuous.