I am assuming the plant you actually mean is Euonymus alatus 'Fireball' - this variety only reaches 4 feet and is relatively slow growing. If you have all 3 in one pot, you need to either give each one its own pot, or plant out separately in the ground, allowing enough space between each for proper growth, as soon as possible. You haven't said how tall the stems are, so its difficult to say whether, and how much, you should cut them back by.

Thanks for your advice. The plants are in a metre long plant pot and are at least 30 cms apart. At present they are about 40 cms tall and do not look very energetic. i will not be planting them out until April - frozen north up here - but i think i may give them a trim even so before then. Cheers.

If they're in a metre long container, I'm assuming that's a shallow container, something like a trough or a window box? Best moved into something deeper, so I'd plant them out asap.