Can I do it online or do I need to go to the polish embassy?
I doubt on line but a visit to a embassy can help.
Should I get a lawyer?
Lawyer from where(Poland or USI mean)I got my kids through a Polish agency in early 2000s but times are different now.
Looks its easy in your case as you can have 3 birth certificates and passports copies(very important) to prove,just get your birth certificate translated in Polish and you are a go.Now a days may take you over 6 months but easier then most people.
What year your parents emigrated and when were you born?
Yes it does depend on it.