permissions between computers

Help, anyone

I have an iMac (let's call it A) and a Macbook Pro (B), both running on Yosemite. (A) holds all my working files and the (B) is linked to (A), either on a local network or via WIFI. I am having big issues with permissions. Let's say I create a new folder on (A) whilst using (B). If I then switch computers and try to make changes to the new folder on (A) whilst using (A) I have to enter my password. Even though the file is on my own computer. The same happens the other way. If the new folder on (A) is created using (A) then (B) does not have permission to make changes to this.

Basically I want full access to all files for both machines regardless of which one created the new folder. And I can't seem to work it out...