1) To me, the British "aunt" sounds different from the British "aren't," but I'm not sure I can explain the difference. "Aunt" feels like a lower, more o-like sound to me. Maybe someone from the UK can explain the difference (if in fact there is one).
2) Yes, "aunt" and "ant" can sound the same in US pronunciation. However, the word "aunt" can also be pronounced with a different vowel sound, which sounds much like the "aw" in "lawn." (This is the pronunciation I use, personally. I don't pronounce "aunt" like "ant.")
3) Right.
Thanks Su.Ki. , now the British perspective is crystal clear.
The problem is the huge variety of regional accents in the UK and , although online dictionaries are extremely useful because you can actually listen to the pronunciation, they usually only provide two different pronunciations at the most (American and standard British pronunciation, which,I guess, is the Southern accent).