Whereabouts are you? There may be little nutrition left in the grass by this time of year, they may need hay anyway.
When I had Mules on a Northumberland moorland farm, we were advised to feed concentrate for the final two months of pregnancy because the ewes wouldn’t be able to eat and digest enough hay for their nutritional needs as the lambs grew, both making demands on the mother’s body and taking up a lot of space, so leaving less room for forage and its digestion in the rumen.
Charollais lambs won’t be quite as big at birth as the Texels and Beltex we had.
Ewes need extra sugar in the last six weeks of pregnancy, so giving them molasses is a good idea - usually a molasses lick, which you’re planning to give them anyway.
We used to feed the Mules 1lb per head per day of concentrate from 8 weeks out to 4 weeks out, then double it by feeding it twice a day for the last four weeks. Conditions were fairly extreme up there, though