My sister is taking advantage of my DM kindness

[autumnbreeze1]

My sister has 2 children one 2yo and the other 6 months old.
My sister basically cannot cope. She couldn't cope with my nephew on his own to begin with but decided to have my niece so close in age. I do love my sister but i feel her and her DP take the piss out of my DM and uses her kindness as a way of my DM always running around and helping my sister. Dsis is either always round my DM and vis-visa. My DM has told me how tired she is, how mentally draining it is to constantly be running around after a toddler and helping look after my niece.
Some examples are Dsis will ask DM to look after both children while she gets her hair done. Dsis will be gone 6+ hours. Or she will ask DM to look after children so she can look in charity shops!! Another time DM looked after niece will Dsis took nephew out with her friend. She was gone all day, no text to DM about what time she would be home.
Even my BIL takes the piss. Dsis was in hospital was niece and BIL wanted to do something with my DF. DM was really poorly but BIL kept asking DM to look after nephew so he could do what he wanted. Luckily DM refused and she was really upset that BIL didnt care that she was poorly in bed.
DM drops anything shes doing at a drop of a hat to help Dsis. Reason being Dsis will get in a mood and not speak to her. DM gets scared Dsis will cut her out and stop her seeing her grandchildren.
Regardless of how ill Dsis and her family are she still insists DM helps her even if DM gets really poorly from it. I've told my DM before that me and DS are ill so please don't come round as I wouldn't want her to get poorly. But Dsis doesn't think about our DM getting poorly when it comes to her.
Dsis did have a nanny to help her 2 days a week but they couldn't afford it anymore.
I feel so sorry for my DM, most of her life is currently dedicated to helping Dsis raise her children and i can see how tired DM is.
When Dsis got rid of the nanny I did offer to help her and said a few times i would. She hasn't taken me up on it though and just wants our DM to help her instead.
Don't know what to do/ dont know if theres anything i can do.

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All you can do is support your DM to deal with any fall-out as and when she decides to start saying no.

Thanks, I have a feeling she wont say no though :(

Your sister knows you would call her out on it. That's why she avoids taking you up on it and goes for the 'soft target' instead (AKA your Mum.)

But be careful. My sister was very similar. I called her out on it and she hasn't spoken to me for almost 5 years now. And my Mum is still running around after her grandchildren because otherwise she 'might not get to see them' (as I am not allowed to now).

Manipulative cow. (My sister.) And sorry but your sister sounds very similar!

Either tell your sister to stop hounding your mother for childcare, and suffer the sulking that will follow. Or tell your mother she needs to speak up and stop being so available to your sister. Not much else you can do.