Alright, here's the happy and not very exciting ending...
I drove by their house two times and didn't see anything. I decided to try one more time. As I'm approaching the house this little firecracker of a woman that's about 5'4" comes running out and motions for me to stop. I stop and she motions for me to roll my window down.
She points her finger at me and says, "Why are you always parked at the gym?!?"
About this time her husband walks out. I said, "Are you Michael and Milissa XXX?" She says, "Yes, Shane, we are. Now why are you always parked at the gym? Me and the ladies that work out in there are freaked out because we think you're stalking us."
The husband then explained that his wife called him from the gym and told him to come get my plate number, so that's what he was doing when he was taking pictures. He explained that the reason he sped off when I got out to talk to him was because he had his daughter with him and he wasn't sure what I was going to do.
I explained that I'm not stalking the women at the gym, but that I sometimes like to park on the street overlooking the pond at the rec center and just unwind and decompress a little before I go home. The husband said he completely understood and had done the same thing.
Basically, they thought I was stalking them so they stalked me. Then I caught them stalking me so I stalked them. Then they caught me stalking them and once we all realized what was going on we laughed about it and shook hands and went our separate ways.
So, there's the happy ending all wrapped up with a neat little bow. Thanks to everyone that was able to help me find them.