Tier 2 Dependent extension

[Bapurao]

me as an main applicant has submitted my Tier 2 general extension application by employer third party to home office on 08-nov-2018. my 1st BRP card will expire Jan 2019. at the time of my submissions we did not submitted my dependents wife/sons application. now visa service provider is saying that I should not submit my dependents application until my visa extension application get successful which will take 6-8 weeks.

1) what will happen if i submit my dependents application with my current BRP
2) what kind of documents are required of my dependents for extension of their tier 2 general application from UK

[Bapurao]

Hello Sir

I hope some one find few time to provide me some suggestions on my query.Many Thanks in advance.