As somebody who does a fair bit of interviewing on the federal civilian side for senior technical positions, I'll offer up some info. I'm on a phone so it may be kind of weak and not fully fleshed out.
First, the interviews can actually be an opportunity to let them know what the job is. Sure, something went out on usajobs but does it match up with what the day to day looks like? This can also be a good spot to introduce whether they'll be working on a team, office structure, etc. It's really their only opportunity to get an idea of what the job is other than at the end if you ask if they have questions, so sometimes it takes up more time than the questions themselves.
Second, you can do 10 questions and fill an hour and make everybody suffer or you can do 5 and take half an hour or less. You don't have to use the corporate questions but you need to know what you need for the role. On paper it's one thing, but in office it may be something different. Do you need firm technical skills? If so, make a majority of the questions technical and make sure they are as good as they say they are on paper. If you are looking for soft skills and team cohesion type role, team lead, contract manager, you may not need to be so technical oriented on the suite of questions, but definitely should ask a few technical questions in those domains.
Not knowing the role or any of why they're hiring, I'll say for civilians... The whole what did you do when your management told you to do something you disagreed with can be helpful. We've had people straight up tell us they did what they wanted to do, and despite aceing other questions that one was a hard pass. Also, why do you want this job. I've had people tell me they want the job for the move to Denver and that just leaves a bad impression that they just want a government paid move. These are gov employees after all.
I will say that if the 4 folks on your list have passed under the new SME review rules with a panel and them ranking 80% or more, then you probably have seasoned technical folks and can focus more on soft skills. Honestly just make sure you ask the questions that help you decide whether this person can do the job and that would work well with others (if needed but important for teams).
As far as questions delivery goes... Federal interviews can be incredibly cold. There are lots of rules about providing the same interview to each person interviewing. That doesn't mean the experience has to be the same. I would encourage you to take advantage of an opening from the interviewee when they mention something to ask deeper or get them to open up with a follow-up question (that sounds neat, can you tell me more?).
Lastly, for now anyway, you can always recommend follow-up interviews if you're not sure. Let the hiring manager know the pros cons of each candidate and punt the decision up the ladder if you can't make up your mind and don't have a preference.