A =26-30", B = 44-48", C = 26-28", D = 22-28", E = 8-10", F = 12-16". Realize, that these can vary somewhat, depending on the size of the child. You didn't ask the seat height from the front runner...that should be 10-12".
I'd actually make the cradle longer than 28", personally. Maybe 30-32". Having kids born at almost 22" they would have been too big for this in less than 6 months if only made to 28". I guess it all depends on how long you anticipate it being used and how big the babies are but I'd err on the longer side, if you think there will be space for it.
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