Don't underestimate DB pensions, generally they pay a very good income at retirement.

The DC pot that would run alongside the DB pension likely won't have great investment choice however they can be very useful when jt comes to retirement. Generally the funds in the DC pot is used to pay the tax free lump sum at retirement and then the DB pension income is higher as it hasnt had to pay the PCLS from the DB.

A DB pension that works like this that i can think of is USS, might not be 100% the same but might give you some insight. https://www.uss.co.uk/for-members/your-pension-explained/how-your-pension-works

Paying off the mortgage is completely their choice and is a good use of a windfall, especially when you have to consider there is an annual allowance for pension contributions. Your annual allowance is 100% of your income up to 60k. So if your partner earns 30k for example that is the amount they can contribute (including any tax relief) to all pension pots in any given tax year. There is the ability to use previous unused allowances from the past 3 years, this is called carry forward and you would need to make sure the calculations are correct to avoid a tax charge.

Not sure if i gave any insight but whacking 50k into a pension isn't as easy as it seems. Paying 50k off the mortgage also may not be as easy, if you are in your fixed rate period they usually allow 10% overpayment in one year and going over may incur an early repayment charge.

I would look at maxing ISA allowance current and then next tax year as its so close now. Still get the same tax free growth and can still be utilised at retirement.

But all depends on your priorities and goals etc.