Skilled worker dependant Extension, Main Applicant already got ILR

HI
I am applying for my dependant extension and needed little help. I was on Tier 2 skilled worker and got ILR last year Aug 2022. Dependat was on skilled dependant visa expiring in Aug 23 and now I am applying dependant extension on same skilled dependant route
Q1: Can I still apply for skilled dependant extension?
Q2: When I filled application and went to IHS payment it is asking for "work start and finish dates" but mine was starting from Aug 2020- July 2023 so what should I put in? same dates and will it ask me to pay IHS on previous dates?
Q3: Second question is "when dependant visa is expiring"but now I am on ILR visa and have no expiry date and preivious visa was expiring on 31st July 2023
Any guidence?
Thanks

Q1: Can I still apply for skilled dependant extension?

Yes.

Q2: When I filled application and went to IHS payment it is asking for "work start and finish dates" but mine was starting from Aug 2020- July 2023 so what should I put in? same dates and will it ask me to pay IHS on previous dates?

Just put a date of 3 years in the future from the date of application to calculate the IHS for 3 years.

Q3: Second question is "when dependant visa is expiring"but now I am on ILR visa and have no expiry date and preivious visa was expiring on 31st July 2023

Put a date 3 years in the future.

thanks