The "possible suicide attempt" came not more than a few minutes of arriving on scene. Based on the reading of the call log the observation of the officer (329) of a possible suicide attempt had to be from some distance from James because it would be a little over a minute later when another officer (325) makes the observation of multiple rounds spent which means the officers were much closer to James at that point. If there were multiple visible rounds but Denise was not visible from where the officers found James (i.e. in another room) then it would be a very good bet at the time that they were not dealing with a possible suicide with respect to James. It seems from the next entry 1 minute later where yet another officer (317) requests the Emergency Response Team (tactical team) that suicide was no longer the operative situation (at least with respect to James) as you don't call in such a team for a suicide as the event is already over. That the log doesn't reflect a change until later is irrelevant as the actions and activities indicate that law enforcement was working the situation differently.
Also, at that time around the initial assessment no processing of the crime scene occurred, no analysis of the crime scene occurred. They hadn't even cleared the house, let alone found Denise at that point. They wouldn't be able to absolutely rule out a murder-suicide until they could be certain that there were no guns found. That couldn't be done until the scene was processed and photographed and some forensic mapping was done before they could move the bodies or items with evidence on them to see if a gun was under any of them.
We don't know what the situation was with Denise, whether she was shot multiple times or not. For example, if Denise had only one wound, or only one obvious wound, law enforcement wouldn't be able to know just from simple observation whether murder-suicide was still on the table - with Denise being the shooter and a firearm being under her or under something else that couldn't be moved yet.
So, all in all, I wouldn't put too much stock in an initial observation (from a distance) as the log reflects two hours after the initial observation that they were indeed dealing with a homicide.