We placed our 4-yr-old GSD in a new home a few months ago. He was extremely obedient at the time but when he was returned, our GSD made a complete turn for the worse. Can you help us?

I have a problem that I'm not sure what direction I should go in here. I have a 4 year old GSD that I brought into our home at 10 weeks old. We placed him in a new home a few months ago, at the time his new owner picked him up he was extremely obedient, and very responsive, and had an excellent temperament. The person that took him, took on a new job and no longer had the time to spend with him. So "Jackson" is now back in my home with my family. I have 4 children, 11, 8, 7, and 18 months. Before he left he did excellent with the kids and my other dog. Now he is being aggressive with my other dog, and he has a nasty attitude with my 18 month old. His obedience is awful, his response is terrible, and I don't like his temperament at all!!! He has made a complete turn for the worse. I've kept him separated from my other dog, and the little one since I noticed this. Is this an issue that can be corrected? Or is my best bet to find him another home as a "only pet" with no children before its to late? Any help or suggestions are greatly appreciated.

Thank you,
Dustin