I think you need to sit down with BF and have a heart to heart talk about how precious Pepper is to you and that you want to make sure you keep her safe and insist that she is tested before all shots no ifs and or buts. Point out that his Dad tested before getting insulin so why would you not test the cat? If he resists, ask him if he'd give insulin to a human baby without knowing it was safe to do so. I'm betting the answer will be a resounding NO!
Now take some deep breathes and try to remember this is new stuff for all of you and nothing horrible is going to happen if you didn't get all the insulin into Pepper and she wasn't tested before hand. This is a learning curve and you need to be as patient with yourself and BF as you are with Pepper.
It's up to you how you want to handle the shots but if you have the advantage of having two in your household who can/do give shots, just make sure you keep a record somewhere so that a second shot doesn't get given or shots are not missed because someone assumed the other gave it. Clear communication is key to ensuring Pepper's safety.
Sometimes you will feel skin resistance when you inject and sometimes not so much. That doesn't mean the insulin didn't go in so never ever give a second shot. Check for any wet fur after you inject but don't massage the injection site. Just lightly run your hand over the area to see if there is any wetness. If you detect some wetness, note it on your SS as possible furshot (FS) so that you will know it may gave been a partial shot if Pepper's BG seems off that cycle.
More deep breathing......