If he is giving his address to someone, he says:
1. "I live at Block 101, East Coast Drive, #10-56".
If you were, say, giving directions to someone to find your place, you might say,"... and drive down East Coast Drive to the corner of 6th street. I'm on the left, in Block 101.
You live at an address; you live in a particular building - "I live in Block 101."
(It is not to do whether you are the residents of the flats or not. I could equally say, "John lives at Block 101, East Coast Drive #10-56."
Where it gets tricky is when you partly give an address, and partly give directions referring to the building in which your actual flat is located:
"I live at East Coast Drive, #10-56, in Block 101." , and one of