Question: Ang/ng or Si/ni for people referenced by their relatio

Question: Ang/ng or Si/ni for people referenced by their relation (tatay) or title (pangulo)?Hello, I am wondering which marker I use when referencing a person (usually denoted by si/ni) with a noun or title (usually denoted by ang/ng)Which is correct?
"Nasaan si nanay" or "Nasaan ang nanay?"
"Anong sabi ni pangulo?" or "Anong sabi ng pangulo?"