In the topology page on the GW, make sure your interfaces and topology for those are correctly defined. External interface is one where default GW is set. The rest are internal. Make sure the first policy you apply is ANY-ANY-ANY-ACCEPT.
On your fw gws, to on ssh/console and run "fw unloadlocal". After you did, on MGMT check SIC is working. If it is, fetch interfaces with policy, then push policy as described above.
Best, look into Check Point for Beginners series, we discuss setting up GWs there in the Network security section. I have provided you the links already.