Multi Entry Schengen Visa for UK ILR holder with Indian Passport

Hi,

I am after some advise on multi year multi entry schengen visa for my spouse as they hold Indian passport and on UK ILR since 2011. In 2008 and 2019 they had visited europe but on single entry visa for few days (had obtained from French embassy).

we both have two kids with UK passport including myself.

Now that the holidays in the UK are not overwhelming, we are planning for European holidays during school holidays and hitting a brick wall with my spouse's Indian passport.

My wife's in full time employment for nearly 2 decades in the UK and have a joint mortgage on our home that we're living in and they're also a high rate tax payer in the UK. I am wondering if anyone can suggest how to obtain a 5 year (or 2 year) multi entry schengen visa
1. which country is the best to approach for this scenario
2. how long the process takes
3. what is the fee and documents would be required.

anyone in the similar boat please respond with your success stories.

thanks,
Bal.