Randy has a video on this. I would recommend rather loading them into the same pen in whatever concentration you like. These are sold as blends, so presumably they play well together in a single solution. TBH, loading that many syringes would suck for me. I’ve done as many as 3 for my bride’s rat and even 2 a day is a pain in the ass.
FWIW, I have done as many as 6 pins in close proximity, e.g. 3 o’clock 2” away from navel, without any major issues. Just rotate locations every day so you aren’t pinning the exact same spot, and if you get ISR, give that area a break.
Embrace the pen!