Maybe, but you need to think about how close they would be to house foundations etc. Up to a point, it depends on which variety you've got, but willow roots are notorious for doing damage so you need to plan carefully.
Is your mum thinking of the damage that willow roots can do? All willows have questing roots that will search out water, so it is not a good idea to plant them where they might get into the drains and cause damage.
::Looks askance at willow in neighbour's front garden::
John Innes is a compost with more nutrients than the usual multi-purpose. Yes, they can all go in the same pot outdoors and then next year they can be planted in the garden. In fact, if you're impatient and because willow is so vigorous, they can probably be planted in the garden now, but growing them on for a year gives you a chance to check that they're all going to grow - quite often cuttings start well and then perish.
Everything I've mentioned should be on sale at a nursery or garden centre.
Thanks Maud....what's John Innes though? Where do I buy that? I've got some compost...got pots but no grit....do I put the pots outdoors? All in one pot? And how long do they stay in there? So many questions! Sorry! I'm a total novice...all I can do is hanging baskets!
Each one could potentially grow into a huge plant, so don't plant them too close together.
You could grow them on for now - you need a medium size pot (6 inches across, say) and multi-purpose compost mixed with some John Innes and grit for drainage. Plant the rooted stems around the edge of the pot (this helps root development) and keep them moist but not soggy.