The first blank corresponds to the world Síganme which is the imperative form of seguir.
The second blank corresponds to the world dígame which is the imperative form of decir.
Let me also translate the text for you:
Agent: well, you already saw the garden. Now follow me/síganme I want to show the inside of the house.
Cecilia: Wow! such a beautiful hallway! there is a lot of natural light here, but tell me/dígame Mr. Orozco, there is only one entrance?
"será" refers to "him"
"serán" refers to "them"
"seremos" refers to "us"
"serás" refers to "you"
Not sure what uds means so I'll leave that
The answer is el but it acctually depends on what and who saying it and who their saying it too
The answer is the first one “Testificariamos”
