Hi YG, been thinking of you such a lot x
My mum died when my youngest sister was young (13, so a lot older than your girls, but still a child really) and we got a lot of help from a local group called Brambles TRust. It was similar in style to Winston's Wish - gave the kids (Of all ages) some head space, a place to think about their bereavement w/out having to worry about further distressing parents etc, and importantly helped them to have fun too. Your girls might well benefit from this sort of support.
We were referred to this group by our GP. Yours may have info on locally-based stuff of this sort.
You are being so strong. Hope you find help you need.