Yorkie .... I'm no longer a single mum, but was one for 9 years.
Obviously, your situation will be rather different to many other single mums because the girls' dad is no longer around through absolutely no fault of his own. And because of the shock of him dying, many of the emotions you'll all be experiencing in times to come will be different to those experienced when a couple split (though not all).
Because of that, I hope you don't mind me suggesting CRUSE to you if it hasn't been already ..... 'cos the people there are experienced in helping the bereaved and, they can also help with a death from a child's perspective. Their helpline is 08701671677.
Practically, the best tips I can offer to cope with life as a single mum is never be too proud to ask for help (they can only say no) and don't be too proud to turn down offers of help you could actually do with (I'm not suggesting you'd actually want people doing everything for you).
I found that by and large being a single mum wasn't too dreadful but the worse times were when I literally needed another pair of hands - and of course there weren't any - or, when I was ill, yet still had to do everything myself.
Lots of people here have already offered their help and I'm sure it's 100% genuinely meant. So that's another tip ....... if you get "stuck" with anything, don't hesitate to come on here and ask !!
I hope I've not inadvertently upset or offended you by suggesting CRUSE. You know as well don't you that if you need to rant, or moan, or cry, or anything really, that there'll always be people here to listen and respond, no matter how trivial you think a particular concern might be.
Other than that, it's quite difficult to offer a "how to be a single mum" guide because everyone's circumstances and coping mechanisms are different and we all need help with different things. So - as and when those things arise, just ask.