Hello,
It is possible to synchronize up to 5 x LM5576 together, with the one set at the highest frequency as the master, but they will not current share. So their outputs can't be tied together. They all have independent control loops and therefore can't be set as a master-slave configuration. You might want to look into the LM5116 which is a high voltage, high current buck controller for your solution.
Best Regards,
-JPF