Dilemma in picking a maid of honor and what to do about flower girl/ring bearer?

I'm engaged and this is my second marriage. I have three children, ages 20, 17 and 10 with the 17 year old being my only daughter. We really want to involve the children, we're more or less having an actual ceremony for them, we would both like to elope but we know how important the ceremony is to them. My first dilemma is this: My only sister was my maid of honor in my first wedding but now that I have a daughter I'm wondering if I should ask her to be my matron of honor, I think my sister would be understanding. We don't know yet if we're having more than one attendant each, we're trying to keep the wedding small and within a tight budget. I have no idea yet how to incorporate my sons into the ceremony but obviously neither one is of ring bearer age. Neither my fiance nor myself have a niece or friend with a small daughter so we're not sure what to do about the flower girl plus between the two of us we have FOUR nephews that are all of ring bearer age, how do we figure that one out? I'm trying to keep this simple, but it's taking on a life of it's own, any advice would be GREAT! Thanks!