one DC - I would put some in to a Junior ISA intended for their higher education, or going towards a car or home deposit. You can put up to £9k in per year.
PCP on car - I would ask for a settlement figure, see if you can get something less than it would cost you to keep going to the end of the agreement and then buying it. They pay not offer anything good, so put money aside to pay it off at the end of the agreement if you intend to keep the car.
Circa £5k in savings - that sounds a bit low. I would bump that up to being 6 months of expenses. You never know when you may need some money to pay for an unexpected expense.
I pay into a defined benefit pension - look at how your change in working hours will affect that.
DH pays into a defined contribution pension - find out how much is being paid in, it may be minimum amount. Aim to bump it to 15% for his contribution.
I have student loan of about £18k, pre 2012 version - as you are employed I would not be in a hurry to pay that but it does depend on your income. Look at student loan calculators to get a feel for how much this is costing you in interest. www.student-loan-calculator.co.uk/
Mortgage wise - it's in two parts, £70k at 2.73% fixed until August 2022 - can you repay £70k in August?
the other £160k fixed at 1.69% until Dec 2025 - I would overpay that at the max you can given the agreement.
Anything left I would invest using your ISA allowances... you and DH have £20k ISA allowance each (assuming none already used). Invest in a global tracker or global mixed investment. Spend some time learning about investing, it's as hard as you may imagine.Podcast: How to choose a mult-asset fund
Depending on how you came into £120k, I would enjoy some of it and give some of it. If it is an inheritance think about how the person giving it would have liked you to use it - spend some, invest some, give some.