I messaged you too, but reading others' responses made me want to chime in a little more.
I have a chart that I can email you--it has columns for feedings (we'd write down which breast each fed on, how long they ate for, then when they started taking bottles we'd write down the ounces they each ate), diaper changes, medications etc. I remember being so sleep deprived and tired when they were teeny that I couldn't remember who I fed last, who had their meds, and who had pooped when. I used the chart and had it three hole punched in a binder that was near where I typically fed them. That helped with keeping track of everything, but also allowed my husband and I not to wake each other up to ask if someone had their meds or whatever. Pretty much everything they did for about the first 4 months of their lives was written down. Eventually we phased out the chart as we got more sleep.
Now that they're older, when they get sick we use marker boards to keep track of who had Tylenol or Motrin at what time, any vomiting, loose stools, etc, since it can be confusing when you have two little ones sick at the same time!
I agree with one of the posters who said to get them on the same schedule and feed them, put them down for a nap, diapers, etc at the same time. It'll take some time but they'll sync up and it will make your life a LOT easier, especially since you have older ones too! Schedules are important--keeping feedings and naptimes and all that to approximately the same time every day will help save your sanity.
Anyway, message me and I'll send you my chart. Hopefully you find it to be helpful!