What can you conclude based on these facts?

It might be easy to conclude that Cesar lives in Cebu City but it should be remembered that the given says that MOST of the Montano family live in Cebu. There is no guarantee that Cesar is one of them.

Since we are not sure if Cesar lives in Cebu, we also cannot conclude if he celebrates the Sinulog festival. If he is from Cebu, then he might be one of those who usually join the celebration but since we cannot make a conclusion based on the details, we can only speculate. There is also no guarantee that all of the Montanos celebrate the festival because there are not enough facts available.