".... Could someone please let me know which bed the squashes
(marrows,pumpkins in particular) belong in a Aliums/Brassicas/Legumes/Roots
rotation system...."

Not being funny, try the compost heap, they will grow so fast on it you wont
want to stand still by it incase they grab you.

Otherwise which ever one you have room for them in


--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk