Water leaking from concrete slab porch into rooms below. How do I stop the leaks?
Concrete always cracks and is porous to water.
What you have is a roofing question.  The only line of defense is what's above the concrete, and it better be elastomeric to account for crack expansion and contraction. 

These rooms are likely not insulated.  A spray foam roofing material applied above the concrete may be just the answer.  The foam will easily absorb the crack motion below, AND give you quite a bit of R value per inch in insulation.  You'd then need to build a new porch surface on top of the foam.

Or look for products designed for walking rooftop decks. Rubber Membrane Flat Roofs (EPDM) for example, you'd basically glue a giant sheet of rubber on top of the porch.  You'd get no insulation, but your water problem would be solved.

Yes there are crack injection kits meant for radon or foundation work.  You could inject the two cracks you know about today.  But you can't inject the crack that will form next winter.  Your only sure solution is a membrane roof on top of the deck.