General Tourist Visa Application -- Tier 1 General

Hello,

Has anyone holding Tier 1 visa done an application for parents to visit UK recently? I have a lot of questions. The online application does not have any guidance document to help with the queries:
1) Can I do 1 application for both mother and father, or do I need to create two separate ones?
2) How many times do they have to visit in person -- 1 or 2? I am confused. Do they have to go once for biometric and once for interview? Also, what about collecting the documents?
3) Do they have to get a TB test / certificate?
4) Does anyone have list of documents you had to send and templates used to invite them?
5) What other documents Parents should take from their side?

Any / all help is very appreciated.
Cheers