The regex I used was
[a-zA-Z]{2,}[a-zA-Z ']*
It seemed to work:
Ouch this totally 'sux0rz - false (numbers)
Ouch this totally 'sux.rz - false (improper character)
Ouch this totally 'suxorz - true
a - false (not enough beginning letters)
a' - false (not enough beginning letters)
a ' - false (not enough beginning letters)
a b' - false (not enough beginning letters)
a'b - false (not enough beginning letters)
ab' - true
ab ' - true
The reason that you were having problems is because you weren't allowing for letters after a space or after an apostrophe. The regex string you created assumes that there is no input other than a space or an apostrophe after a space or an apostrophe.
Greetings.