I've got a question about Patronus'

Not at all. Harry and James' patronus' were the same. How could they have the same happy memories when they are total opposites and grew up in totally different worlds? McGonagall and Umbridge also have the same patronus, and they most certainly don't have the same happy memories.

Harry tells everyone to think of their happiest memories to conjure a Patronus.

What shape their Patrunus takes has nothing to do with memories. It should depend on their personality and things that are important in their lives. Tonks' Patronus changed you see. It wasn't always a werewolf. Falling in love with Lupin made it become one.

Anyway, I guess the shape of a Patronus Rowling gave a character is just another layer of expressing his/her personality and subconscious.

Definitely not. It has nothing to do with having the same memories.

Delamico is right, they have the same patronus because intense love can cause someone's patronus to change. Tonks' changed to match Lupin's and Snape's changed to match Lily's.

As for Harry, either the patronus can be inherited or his love for his parents caused him to produce the same patronus as his father!