First, I am still new with goats (just 4 years) so double check before taking my advice.

Plus, many people do things differently.
We dry our does off when they have 60 days of pregnancy left, they all are getting grain, but very very low amounts, (about 1/2 - 1 cup a day), some heavy does may get cut entirely. If they are filled out ok, and not growing 1 - 2-year-olds, you can wait until the last 2 - 3 weeks of pregnancy to start them on grain. Start low (1/2 - 1 cup a day) and work up to about 1 - 3 lbs by their due date.
The main thing I would do is to start now (last 60 days), switching your girls over to alfalfa hay (or pellets), as they will need the calcium and protein from it for growing babies.
We give selenium with Vit E in it (injectable) once at 5 weeks before kidding, and again at 3 weeks before kidding. I do believe Molly (fiascofarm) gives vit E powder daily starting the last 5 weeks of pregnancy.
Hope this helps some, we also have does due, starting Feb 11th through March. Can't wait for kidding!