What Xavier meant by Borgia Residence was a serviced apartment property located in the West of the city. It was located in a complex apartment building adjacent to a mall. Xavier owned several units there under someone else's name and he used them to house his men from out of town when they came here for business.
Even though he owned the units, he made them seem like they were part of the serviced apartments managed by the Borgia Residence company.
This was another thing that Elleard didn't know. While he was in a coma, Xavier had to work with a lot of assassins and people from the underworld. They all needed places to hide during missions and the best place to hide was within the crowd. That's why they had accommodations here and there, even mansions in high-end locations.