How do houses / apartments / condos work in GTA Online?

My friend just bought a place in GTA Online, but I was wondering... Can I purchase that same place (without him connected to my game)? If so, can he still join my game? Will there be any conflict? Are these places considered safe houses?

Solution 1:

Multiple players can purchase the same property in GTA online. Each one is treated as separate sub-instances. Think of it as each of you owning a separate unit in the same complex. If two players are in the same instance and own the same property, they are free to visit each others' specific apartment.

They are considered safe houses. Your cars and character are safe from cops and other players while inside. No one can enter without your permission, and inside even invited players cannot commit any violence.

You can own up to five properties at a time, but you will only be refunded for the partial cost of your old property if you decide to buy a new one