skilled worker dependent visa extension

Hi I am Applying for skilled worker dependent visa extension for my family members

1. My first skilled worker visa started from July 2021, and April 2022
2. I have changed the employer and Switched to new COS started from 18th April 2022 to till 17th April 2027
3. I have got the current COS for 5 years, and my skilled worker valid till 17th April 2027
4. My family (Partner and two children) current Skilled worker dependent visa valid till 25th July 2024.
5. So I am applying for remaining tenure

Question: while paying HIS what option I should select in application is 5 Years or 3 Years? Because my COS is for 5 years but I have already completed 2 years applying remaining 2 year 9 months
If select 5 years, its taking HIS fee for 3 years £3105, but application fee they are charging £1638,

Someone please help