hi ya lawless, how big are they now? have they shown there sex yet? the reason i ask is because if you can see the fluffy bits i'd put em in now, cause WW will stretch to about 3 -3 1/2 feet during the early stages of flowering. but ideally you want to wait till they do show otherwise i believe it raises the possibilty of being hermaphrodite

to top your plants, look for the growing tip between the newest set of leaves on the main stem n pinch it out. fairly straightforward. i'd deffo do that given the size of your space. your gonna have to train them somehow. so top em or use low stress training on them to give you some headroom is my advice. if they haven't shown any sex yet i'd top or train

good luck k