Ideally you would want to mull the units prior to installation.
Consider mulling them on the ground, then removing the sashes & hoisting the group into place with some help from inside & a rope. With the sashes out, the weight will be greatly reduced & very easy to raise by help from the rough opening while you guide from outside.
You can then do a light temporary attachment of the frame to the home & replace the sashes to ensure alignment while doing permanently install. From my recollection, the sashes can be replaced from inside, meaning you wouldn't have to haul them up the ladder. Good luck