If I remember right, the one preparing the tea remains seated throughout since its bad manners(?) to even kneel.
You stay seiza for the whole ceremony; although if you are inexperienced (or male), it is permitted to begin in seiza and switch to sitting with you legs to one side later; this is, of course, not applicable to a more formal ceremony, where all participants are supposed to remain in seiza the entire (up to 4 hours) time. This is because you're really supposed to be in a kimono and it's a bit unsightly to be in anything but seiza when sitting down. (Men can be in formal suits, unless, again, it's a high-formal ceremony)
The Admiral should be in seiza, but can lean forward to pour as long as her legs remain on the floor.
You wanna have a cuppa too, Admiral?If you pour it in the English style - from a bit of a high position - it's delicious, see!I've brought round our New Face, Warspite!plsssssh...Oh? You want in on this too, Hamakaze?You can sit in seiza, right?I see.
An eclectic Anglo-Japanese style wouldn't be half bad. But, it'd be a bit tough without half-sitting, wouldn't it....Since we're going to all this trouble, why don't we have a Tea Ceremony?It's the bee's knees!Oh~ Yamato Nadeshiko!...no, for the purpose of a greetings, let us prepare some Japanese tea.
Go get a teapot.