that vs. who.
My sister, who lives in Poland, has two PhDs.
My sister who lives in Poland has two PhDs.
My sister that lives in Poland has two PhDs.
The second and the third have the same meaning (I have 2 sisters).* The first has a different meaning (I have one sister).**
As you can’t use commas in speaking “that” is important for clarity.
So don’t tell me to say “who” when I want to say “that”.
*defining relative clauses
*non-defining relative clause