You should be able to log in with the gmail that was on the phone
Adding to what was stated, that setting up a new Gmail account does not override a lock code on a device. You would need the unlock code to gain access. I would suggest asking your brother for the unlock code if he knows it so you can to gain access. The other option available would be doing a master reset. This erases all the data on your device. Perhaps once your brother realizes what will happen to your data, he may cooperate with giving you the unlock code making it easy and avoid more issues.
Here are the steps below for a Master Reset:
1. Power device off
2. Press and hold Volume Down and Power button at same time until screen displays with 3 androids at the bottom
3. Press Volume Down down to highlight Clear Storage, press Power (PRW) Button to select option. The screen displays below information to clear storage with you selecting the option.
4. Delete All User Data?
A. Volume Up for YES.
B. Volume down for No.
After this has been done, just go back and set up your Gmail account again and sync your information to the device. Since you set up a new Gmail account, please use the Gmail account you had before your made the new Gmail account. The former Gmail account should have your information before the incident took place. I hope this helps.
I believe you can reset a pattern without a master reset if the pattern is forgotten. let me check it out and get back with ya before the dreaded master reset.
I added a pattern lock and purposely ran the incorrect one. After 5 times I had to wait 30 seconds. I did, and ran the wrong one over and over and over. And each time there was a box, "Forget Pattern??" I clicked on it and was offered to enter my GMail address. Look for that box in the lower right hand corner.