It really is 'how long is a piece of string'? on this one.
Cats are territorial pack animals, so a new cat has to slot into the pack. Some cats do this quite easily, either by taking up a place at the bottom, and not getting in anyone's way, which causes minimum fuss. Others are made of sterner stuff, and may even think they are 'top cat' and will challenge the incumbent for that position, which means lots of stand-offs, fighting, and general mayhem.
I would be inclined to persevere. As long as your newcomer is not coming off worse in any encounters, or is obviously distressed and not eating, then let them sort it out themselves. Cats do get used to a newcomer in time, and your newbie will either be accepted anf fit in, or a compromise where they ignore each other - as with Barmaid's tribe - and some are quite content with that.
Keep an eye on them all, but know that all the spitting and huffing and puffing is part of cat society, and they will eventually resolve matters in a way they can all live with. If it becomes apparent that your new cat is always going to be unhappy, then you need to think about re-homing, but give them a chance to see what they can do first.