All those are AL-iss-tər to me.
Quentin - KWENT-in
Quintin - KWINT-in
Quinten - KWINT-en
Quinton - KWIN-tun
... but do they sound indistinguishable when I say them aloud? Very possibly!
I think the first syllable E vs. I makes a difference, but the ending makes less.
- mirfak