Ok, so the footprints, "stalking" or morning of the murder, that remains an open question for the time being.
The brother as an accomplice? I'm less sold.
It is EXCEEDINGLY creepy of him to ask for a photo, and I have no doubt he was not asking for it in an effort to help Melinda's family in their grief or to find "the murderer." I'm sure he was trying to get creative, trying to think of anything, to connive to get any evidence he could imagine might do any good at all to help exonerate his brother.
He knew Steve looked guilty, but I'm betting he (at least initially) thought Steve was being framed, or it was all a mistake that would be fixed when the facts were discovered. But I think he's a blind lead. My opinion only, of course, but I think that (like Steve's aunt) Steve's brother believe(s/d) in him and was scrambling to get his brother any advantage he could. Remember, Bro was probably shocked at all of it, too. He was (I imagine) grasping at straws.
What a gruesome picture of the entry would could do in his mind, I couldn't guess, but I don't think he was in on the murder. Blind to the obvious maybe, but again: family. His brother. Murder. No way could he believe that, not that early on.
Now, if the shoeprints were in the snow at the "stalking," that's more up for debate in my mind - but I'm leaning against it. If Bro knew that he was complicit in gaslighting Melinda immediately prior to her murder, and he did it at his brother's behest, I don't think he'd be as quick to be helping Steve after her death. He'd be thinking, "Whooooaa...what if...and...??"
I think he'd be trying to put & keep miles between them. Again, my opinion only. I just think he's a patsy. Steve used him because he knew his brother would go to the mat for him. How many of us have a family member we believe could have been capable of killing AND still keep them in our lives? It's one thing to know we have a Bad Apple in the family (drugs, affairs, lying, unreliable work history, etc.), I think every family has one or two black sheep, but believe your sibling could MURDER his wife and you go along with it? I'm not saying it's not possible; I'm saying I don't see it in evidence.
Not yet anyway.
I think Steve's in it alone and was trying to use his brother because Bro would look really good because His Brother Is NORMAL - because he was honestly shocked and bewildered and Steve knew he would be. I'm betting Bro's not so sure now tho.
And anyone know about the dogs? Did the vet put down 2 healthy pets? Some will refuse. Hippocratic oath, etc. And did the ex & Steve's boy get their dog back?