You do have to roll with a bit more with 3 - there is no real way of making it as regimented as it is with 2. If you can get a really good nap in the middle of the day then I would stick with that - that's what I was able to do with my third, and the other naps were always a bit more hit and miss. I must confess, he was not a brilliant sleeper, but I'm not sure how closely linked to his nap schedule that was. The key thing is to make sure that you are working on independent settling skills and you will get there in time - they grow constantly and their needs change and before you know it, it isn't a problem. For us, we kept the nap in the middle of the day at the same time rather than worrying too much about A times - the other naps moved a little and shortened, but having the core nap in the middle of the day was a lifesaver for us. It was also the easiest to preserve as coming home for lunch was an obvious thing to do, and the other ones rested at the same time so we all got a break - and tbh we still do it now, even though nobody sleeps (except me! 😜).
Hth - it can be a bit daunting to start out with when you have 3, but you will get in to the swing of it quickly enough.