Hi
the ultimnate answer is you will need to consume and test to see what a particular substance in a particular quantity does to you. How things affect me might be no indication of how they'd affect you. For me caffeine via coffee or a caffeine drink has no impact on BG either way. I take my coffee very strong with cream.
Wines are relatively low in carb - about the same ballpark as beer but not drunk in the same quantity - well, I don't anyway. Spirits are zero carb, but a lot of mixers are variations of sugar solutions. I do not trust the syphon machines that bars use for common mixers. So your gin and vodka in themselves should have zero carb, but the mixers, whatever they are, need to be checked.
For me alcohol itself will lower my blood glucose levels - it appears to interfere with my liver adjusting my blood glucose. This usually produces skewed readings, and these days I won't bother doing a before-and-after test for a meal where I've had more than a glass of wine.
Word of warning - I have had one hypo when drinking after a 24 hour fast. I felt absolutely fine until I suddenly didn't, and although it was bad enough the consequences could have been a lot worse - I have the scars. Please be extra careful with alcohol if your BG is already low or if on BG-lowering meds.