They are not very old to be in with the older hens and mum probably doesn't think it safe for them. Our broody hens leave their chicks of their own accord and move back in with the older hens when they know its time.
Could you wire off a section of the barn for them and leave them in there for a few days ..... no free ranging? They would then learn that barn was home and return there at night once out and about.
If you just move the eglu I think they will get very confused
and you could lose some. Sometimes my son has moved a coop down our lawn when mowing and hens couldn't find it at bedtime.
If you can't wire an area I think it best to box and carry for several evenings as suggested by FW. They would get it after a week or so.