My situation is a little different - our 1st doesn't live with us... I had her at 17 yo, so due to something out of controll she has been raised by my in-laws.
Any ways #2 was easy - was 27 with her & she is more like #1 for us since her older sister wan't home all the time. 15 months later we had #3 which wasn't too bad, we still was one to one & it was easy to keep up with them since we could both just keep an eye on one. #4 was born 2 years later... it was a little harder to find a grove with him. Now they out numbered us as to the kids in the house. So, now were had to keep an eye on more... so there wasn't the one on one thing anymore - if they all took of in different directions it was harder to keep eyes on them and beleive me they liked doing their own thing and running in different directions. It did take a bit to figure out how to make it a little easier... but we did figure it out. 3 years later we welcomed #5 into the mix... that one wasn't too bad after all we had already figured out our out numbered situation. Then 17 mo later we welcomed #6 (and our last) into our family... she has been a great addition although her coming did cause a few issues health wise for momma - well kinda, the disorder was dormant, her pregancy and my age (34 when I had her) just helped to cause it to come to the surface.
All in all - I think having 3 in the house was the hardest transition... but I wouldn't give up one of them to make life easier - although at time I want to run and hide! As I saw someone else say - it seems like atleast 2 of them are always fighting... you know siblings. They are all pretty good most of the time, but with that said, since I have so many little ones in the house (all 8 and under) it seems like at least one is always doing something they shouldn't be & when you are addressing one mishap - another one sees it a a change to get away with something. So, keeping calm is harder to do since it seems like I am always telling someone No, Stop, You know you aren't alloud to do that or What is the rules? Plus, it doesn't help that will the issues from last year I get "frazzled" a lot easier.
I do think the hardest chage is when they start out numbering you. But in is so worth all the smiles, cuddles & l love you's you get in return!
Good luck making your choose :)