Brocoli and cheese is this half a syn? If so if I have half the packet is it then free?

Yes it's 1/2 a syn for the 110g pack and the 99g pack.

Personally, I even if something is 1/2 a syn and I only have half, I will still count 1/2 a syn for it. If I don't, I start to 'forget' other things and that's when I go off track.
I would always advise to still count the 1/2 a syn regardless of how much I have.