This sucks

I need to know how long the cycle is, our male has an appointment and I am wondering if we have to keep them apart that long. His sister just came into heat.

The heat cycle lasts about 3 weeks, give or take. It can be longer or shorter for some dogs. Your dog's vulva will swell and she will begin bleeding and cleaning herself a lot. Once the bleeding stops and turns clear then she is ready to mate and this is the most vital time to keep them apart which may not be easy. They will both likely try and get to each other. If you have an accident don't panic! Call your vet immediately because you can get a mismate shot to null the pregnancy, but you only have a short window to do so.

By appointment do you mean to have him neutered? If so then the sooner the better! It would be wise to have her spayed as well. Your boy won't be the only neighborhood dog looking for love.

His appointment is in 2 weeks, purchased diapers for her today. They have never been apart, going is getting ruff/

You only have this one cycle to keep them apart. It won't be easy but it is necessary.

I feel for you, your little boy is going to go mad trying to get to her.

My mum has 6 dogs at her place, at one time she had 8... All show dogs...

Imagine trying to keep 1 dog separated from 7 others!
Not only that but when you have dogs together for so long their heat cycles start to get into sync with each others, so if one started going into heat, the rest of the females would follow.

Silverfoxkit summed it up pretty well.
Just keep them apart, opposite ends of the house if you can to avoid your male fretting and if you need to bring your male into a room where she has been use some cleaners or deodorizers to help mask her scent.

If things get too out of hand and your male is really fretting and trying to get to her then it's time to ship him off to a friend/relative or even a boarding kennel until her heat is over.