G.~
Your children were exactly the same ages as mine where when was surprised with the news of #3. In my opinion, it's both easier and harder. I think that it is easier to get used to a third one, vs. when you add the second. Adding the second was such a change cuz all of a sudden, you have to divert attention away from that first one, which you only had for 5 years. In that sense, the third one just blends in.
However, when you have 3, there is always something that needs to be done-I feel as if I never stop moving, taking care of the needs of these kids. My house is always messy, not dirty, just messy, and there is always laundry to be done. My second one was 21 months when his little brother was born, and I didn't see too much sibling rivalry happen. He was just so young that he hard a hard time being "gentle". Leaning on baby to kiss him, or he always liked to touch his head to the babys, and it would wind up being almost a head butt. Those first few months were kind of a blur, but I was almost aways able to sync their naps, so that I'd get at least an hour or two a day to myself. And remember, new babies do sleep quite a bit at first, giving you time to adjust. I remember reading somewhere that if both of the little ones are needing something, it's best to attend to the older one first, as the baby isn't going to harber resentment like the older one could. It is a little crazy that first year, having 2 kids that really need mom's help and attention, but certainly manageable. You didn't mention the father much, but I assume he's home every evening. I believe it is vital that he understands that your days will be filled with attending to the children, feeding them, changing them, and cleaning up after them. He will need to either step up and help more with those more obscure chores, like dusting, mopping, laundry, or realize and accept that they will slide down your priority ladder. Like I always tell my hubby "I am a stay at home MOM, not maid!!"
Now that they are 14 months, and almost 3 it is really starting to get fun. The youngest had learned all his motor skills at an alarming rate. I'm not sure if it was to keep up with the other two, or trying to get out of the way, but he's scaling playground equipment and stairs constantly, which keeps me on my toes. The oldest is at school all day, so we are able to still go do those fun "little" kids things, like 15 minutes stops just to check something out somewhere, or walks around the neighborhood. And now, the older two are starting to be able to play some "older" kid things, like cars and house together.
Some of the biggest hurddles are going shopping--having two small kids in the parking lot is stressful. I always park right close to the cart corrals so I can get one right at the car to help free up my hands to get the other one out while keeping that first one safe. I actually prefer to take my oldest with me, as she can hold on to the middle kid, while I get out the youngest. The 2 younger ones share a room, so I have to stagger bed & nap times a bit, and that can be an issue sometimes, but not horrible. They don't wake each other up if the other is in a good sleep.
You will do it, and do it as well as you can, because you won't know any different. Your family will adapt because they have to. And in six months later, you are going to wonder what life was like before #3 was born! I used to thing I was busy before....
I hope that was semi helpful for you. Good luck!