I got engineer from Italy to work in Macau for a project of 4 months. How to solve visa problem ?

Does he have to go out of Macau after 3 month of free period (90 days for Italy)? Any lapse period before he can come back to Macau for another 90 day ? Or he can apply a multiple entry one for 4 months before the project start ? What is his tax liability for working for a 4 month project in Macau?