Came across this annoying glitch today while doing the light's out quest after I killed Deeja and read the note to find out Jaree-ra's location the quest would not update so I just went on ahead to broken oar grotto(which I had already cleared before) to finish the quest, so I go through the bandit-less cave to find jaree-ra alone and quickly kill him but when I attempt to leave the cave my two followers(serana and dark brotherhood initianate) do not follow me out instead they remain near the entrance I have tried dismissing them but they still remain stuck

In situations like that, what I do is simply leave them there for a bit. By waiting around elsewhere for 24 hours, you cause the game to recalculate where the various NPCs need to be, and followers that get stuck tend to get warped to their 'home' point as long as you've previously dismissed them. I've done this several times when Lydia fell into a hole or got stuck behind a rock (it happens), I just dismiss her, wait 24 hours, go back home to Breezehome and she's waiting there in her seat

I guess ill have to try that then I didn't wanna dismiss them because I had somehow been able to have 2 followers at once(probably a glitch obtained by having serana as a follower) but once I dismiss one of them or mainly serana herself it seems to break the glitch hence only allowing me to have 1 again but I guess that is better than having to load an older save and losing 2hrs of gameplay.

Make sure and keep an old save, just in case the method doesn't work. I didn't realise there was another glitch involved, so it might not go as planned, and if someone else posts an alternative method you'll be able to revert back to that point and keep your followers together