Oh what an awful situation to be put in BB.
Can I ask how old you are? (very rude of me I know).

Was this cats pregnancy planned or an accident? Surely your mother should have expected the kittens to be around for a good 8 weeks after they were born when she allowed/found out Victoria was pregnant.

Even if they are not spending time with their mother, you have been acting as their mother by giving them all the care they need, so they really should stay with you (and each other).
Also without being around your other cats, they will find it harder to lern 'how to be a cat' and the new owners may find them very hard work, particularly with using the litter tray.

And surely your mother realises there is enough love and care to go round in your house for Victoria and babies.