That streak of luck means you do both indeed make the save! Natural twenties don't really have an effect on saves, but you are welcome to put some flair to the description once the time comes @Ryonara. For @Zverda, that time is now! Halved damage for both either way.
As a side note, it's going to include a hefty amount of rolls with advantage thanks to the Pack Tactics feature of these creatures. Guild dice are not exactly advantage friendly. Would anyone be opposed to me rolling them with a dice roller bot and linking a screenshot of the event instead of ten separate attack rolls? It certainly isn't as tamper proof, but it is a fair deal more convenient for yours truly.
You attack is successful in cutting down a foe @The Harbinger of Ferocity. You are able to have one sling wielding kobold at best, though then you would also get one of the winged sort next to you for the other target you desired. Would this be acceptable?
Two kobolds potentially trigger an Opportunity Attack from you @The Harbinger of Ferocity. Will you strike the first or the second? Please provide the roll to hit and for damage for your eventual choice! Both Dash, neither Disengages.
Assuming they both move at the same time, Brannor will attack the first, otherwise he will strike whichever enemy moves first. The blade I presume to strike on a total of 20 for 14 slashing against its victim, @Hekazu. Hopefully that leaves this cave and the realm with one less kobold devoted to a dragon.
Assuming if Brannor were to Dash after the kobold himself, would he be able to reach it or would it it be out of reach, @Hekazu? Given it provoked initially I am assuming it could be caught, unless it has a higher land speed. Does it appear to be moving too fast for it to be caught or does it seem like Brannor could manage to threaten it again, assuming someone else does not finish it off with a ranged attack?