Lots of good advice here
Ignatia is a good option to help with emotional stress and grief, like weaning, separation and new environments.
If you think they are ready to be separated from their mothers, then what's to stop you just sending them off?
Both mothers and offspring will be just as upset on initial separation wherever they are, so you might as well have them out of sight and sound of each other.
I personally don't sell my donkey foals before about 9 months as I find they learn a lot about social interaction etc from their mothers and the rest of the herd and to me they are still babies at 5 or 6 months of age. I do not actively wean them, but leave them with their mothers till I decide to sell them. But that's just my opinion.
As mentioned, it will be considerably less traumatic for your 2 as they have each other for company, and the use of Ignatia should certainly help.