Tier 2 extention for child dependent

I currently have ILR obtained (March 2018) via 5 year -Tier 2 General visa.
My spouse currently on Tier 2 PBS dependent visa valid from 19-10-2017 till 15-08-2019.
We had our child born in India in Jan 2019.

I applied for PBS child dependent visa for my child from India on June 2019 and got an entry clearance vignette (Tier 2 dependent visa) upto 15-08-2019. I was waiting to collect BRP but didn't receive it. I was thinking something has gone wrong with my Child BRP card and enquired the UKVI. I applied expecting that my child would receive the visa for 3 years but later came to know ( 319I (a)(i), https://www.gov.uk/guidance/immigration ... #pt8family) that my child visa was based on my Wife's Tier 2 visa (valid until 15-08-2019) expiring today.

My wife applied for her Tier 2 PBS extension last week (August 12) in the UK using normal service. My wife's visa is under processing.

Since my Child's visa would expire on 15-08-2019, I made an online in-country application for my child yesterday for a child PBS dependent extension (biometrics yet to be provided).
Now I have the following question

1. Since my child's visa is indirectly dependent on my wife getting her PBS Dependent visa application. Will it affect the chance of the child getting the Tier 2 extension?
I am planning to write a cover letter along with my Child's application and explain the situation to UKVI. Should that be sufficient ?

2. UKVCAS said my daughter's biometric can be provided before 16 October. Considering that an in-country online application has been made, can the biometrics be provided on mid september ?

Thanks for your help.
Neels

1. Since my child's visa is indirectly dependent on my wife getting her PBS Dependent visa application. Will it affect the chance of the child getting the Tier 2 extension?
I am planning to write a cover letter along with my Child's application and explain the situation to UKVI. Should that be sufficient ?

A cover letter should be fine. Date of application is the date you submit and pay online.

2. UKVCAS said my daughter's biometric can be provided before 16 October. Considering that an in-country online application has been made, can the biometrics be provided on mid september ?

It does say BEFORE 16th October, meaning anytime between now and that date. Simply make the appointment at UKCVAS and enrol the biometrics.

Do you meet the 90 days maintenance funds requirements of 2 x £630??

Thanks CR001,

I have filled, submitted and paid for the application yesterday. So I will follow up with a cover letter explaining my situation.

I have sufficient funds to show maintenance. They said £640 is sufficient, but I plan to show more than that (> 2x640).

Thanks again for your answer.