sleep overs..

I have had my GC stay since they were tiny toddlers but the OP's situation is very different. A family, where the daddy has died, need to be together until they can work through their grief.
Children can fear the loss of the remaining parent and like to keep them in sight.

As has been said, it all depends on the child and the Mum.
One of my grand-daughters slept over from being a toddler and loved it.

My grandson from another family, is 10 and still isn't ready, though he loves spending all day with me.

The decision is always Mum's and child's, no one else's.

My own AC - DDs were about 6/7, DS never - had to collect him from friend when 10 and bring said friend back to ours. DGS1 age 3 when his sister was born and DD had sepsis then him and DGD aged 5 and 2 for DD1 to go to a retirement and DSiL on nights. DGS2 still breastfeeding at 16 months but I sometimes put him to bed in his own cot when DD2 on back shift. He sometimes wakens for a night feed so not ready to be without Mummy all night.

My GC slept over at my place from the age of 3. My gs loved staying here, but my gd was a mummy's girl, and I had a lot of problems, trying to settle her every time she was dropped off (due to daughter going away with work). I tried letting her sleep, sniffing her mum's dressing gown. Gosh it was hard work, and till today (she is 16) I feel guilty for raising my voice at her, when she just didn't stop screaming. 😘

That’s a good age for them to do a sleepover,some of my own DGC are the same ages, and they started sleeping over now and again recently.It has to be tried, to see if it works out.

My DGDs have slept over since they were about 6 and 4, (now 11 and 9), always together and they are a pleasure to have. If DS and DDIL want a night out it is easier for them to come here than for me to go to theirs. And if it's a school day the next day it's me who has to get them up and in their uniform and breakfasted while mum has a more leisurely morning and picks them up at 8.30!

You need to take a step back - it is totally up to your daughter as to whether your grandchild comes to stay the night or not. Don't try to insist on her doing something she does not feel comfortable with as it will probably lead to disagreements you don't need or want.

She probably needs them more than they need her, in this particular narrow circumstance.

But when a child is prepared to sleep over varies a lot. DGD stayed with us for several days at the age of 6. DGS would not sleep away from home unless a parent was present, until he was 9, but he got there in the end.

Just play it by ear, and, as others have said, suggest to her that you babysit at her house.

You daughter has obviously had a tough time, and just isn’t ready, I wouldn’t push it, let her decide in her own time

I agree with TwiceAsNice - if the mother doesn't want the children to sleep over at your place, it can't happen. Offer to go to her place and look after the children overnight there - if she is happy with that , great. It's understandable that she is so attached to the children, having lost her husband. Let her set the rules and go along with her on everything.

Children should sleep over when they and mum think it’s the right time whenever that may be? Varies between children and families.

If she lets neighbour babysit can you not stay at her house to look after them ? They are still quite young and have lost their dad, they are all probably still very fragile . Mum may not want them sleeping in a different house to her yet. Chat and see if you can compromise and have the children when they are older. If you push this you may cause more problems for yourself.