What other option do you have? being a working mum has huge benefits for your kids. being a SAHM has different benefits. You're not doing wrong, unless you or your children are not happy with your arrangements.
What is the relevance to the grandparents living in the north? Do you mean they are unavailable for childcare and so you are reliant on childcare for the unsociable hours which you maybe are stuggling to afford or find?
If you are struggling to find appropriate childcare you can ask your company if they will look at your hours, but if it is a requirement of your job to work shifts etc you may not get fixed hours instead.
If your job is working nights etc between regular times you may be able to find a childminder who will have dc overnight for example.
Many parents work unsociable hours. And not all can rely on family for childcare. If you can't find childcare then you may have to consider finding a different job if your company can't meet your request for flexible hours for some reason.