As long as they are in the shallow end and have arm bands on, and you keep an eye on them they'll be fine. I've been swimming on my own with three under five and it takes organisation but we've been fine.
you will be ok, i have been with a 2 & 4 yr old, plus an 8 yr old ( but he is a swimmer ) - but still got to keep an eye on him. have them both in little pool lifejackets/armbands and stay right next to them. i was a bit overwhelmed at first, but like everything you get the hang of it and it'll be good fun for them. the fact that they can both touch the floor is a HUGE advantage - you will be fine - go for it!!
I've managed it with my 4 + 2yo's (and I am hopeless with them most of the time as they are so spirited). DS has lessons so he's used to the pool. DD ends up plonking herself on a giant float and I pull her round .
We only go early in the mornings when its dead quiet though. We're usually the only people in there. Once it gets busy we get out.
I would check the rules at the pool- some have a policy of 1 to 1 with under 8 yo - whether or not they can swim even if you are in the shallow end- ridiculous I know. My friend could not take her twins swimming alone because of this even once they were competent swimmers.
If there are no such rules where you are then go for it and have a great time!
Definitely check the pool rules - I have been to two pools in the last couple of weeks and both had notices up saying that there had to be an adult swimmer to accompany each non swimmer / child under 8 years...
Funnily enough, one of the pools was one I used to go to as a child.. A gang of 7-11 year olds would go together.. A lot of us were certainly not strong swimmers.. But there were no rules back then!! And it was only 25p to get in!!