Siblings have anger and resentment towards mother. I don't want them to confront our 88 yr old mother when she is literally on her deathbed.

Oh, one more comment...there is NO "inheritance" until AFTER mom is dead. There may not even be a "minor" inheritance if ALL her funds are used for her care now.

I would use their minor inheritance to make things more comfortable for your mom.

Yesterday is gone, it is pointless to demand a "I'm sorry". Who wants something that is obviously not sincere? I, personally, see this as some mental illness on your sister's part. What she did was probably deserved, you know what kind of dad he was, you know what kind of mom she was, but demanding an apology doesn't work.

Maybe just staying out of it would be in your best interest. Can't change anyone that wants to be a victim, as your sister's have shown they are.

My brother wanted to punish our parents for what his perception of the situation was, he gets off on playing victim. Not that it wasn't awful but, he stayed involved with the nonsense and still cries about it, sorry, at 18 you are legally able to change your situation, staying around shows it isn't bad enough for you to be done with whatever the situation is. He liked rolling around in the pigchit and even perpetuated it onto his own children. So very sad.

You say at the top of your post that you don't want them confronting mom on her deathbed. In the rest of your post/question you say mom is doing well.
So I am going to presume (I know dangerous territory) that right now mom is doing well and you are projecting the "what if's" that are in your head.
If your sisters really have anything to say now is the time to say it while mom is "doing well".
Now personal opinion here.....
I have said before on this forum that I am of the firm belief that a person that has been abused should not be a caregiver for the person that abused them nor for a person that allowed abuse to continue.
So...if mom allowed abuse to happen or to continue I get the anger, I get why they do not call or visit.
(I will say that what might be considered abuse now your mother at 88 might think that it was the proper way to discipline or it may have been done the way your father was raised and 60 years ago what the husband said was the final word. That does not make it right though) Given that your mom may not think what your sisters think was terrible your mother might not understand their point.
Now..the question is..Are you POA and are you acting as POA now? If so and if this would upset mom then you are within your right to limit or prohibit communication that is not in your mom's best interest.
If you are not POA or acting as POA at this time you can not limit communication.
If mom is living with you and you do not want this confrontation happening in your house you can ask them to meet mom in a public location and they can talk to her there. If you are living with mom you can remove yourself from the room or from the house while they talk.
If you are worried about a letter that might be sent while mom is on her "death bed" if you are POA a letter like that might be placed on the nightstand to "be read later" .....then burry unopened it with mom.

My advice is to encourage you to understand that you cannot change other people, and that you are not the arbiter of their choices. If your sisters ask your opinion, you can gently let them know that it's too late to settle anything unsettled now. If they don't ask your opinion, I encourage you to keep it to yourself.

I am sorry for your losses, and hope you all will be able to move on.

Don’t try to prevent your siblings from saying whatever they feel they must. It’s not you who must live with their words, what’s said is on them. Perhaps they need to speak in order to heal from something you know nothing of. It’s really a matter you need to stay out of and not discuss with mom or your siblings

Since your Mom is "doing well" -- and presumably this means cognitively as well as health-wise -- you should not butt in to other grown people's relationships. Your sisters feel like they have something to work out with your Mom, so let them try. You need to be Switzerland and be neutral. Your Mom was a great Mother to you? How lucky! Your sisters, for whatever reasons, were not as lucky. Mature adults work things out between themselves. They don't call or visit because they don't have a good relationship with her. Better they work through it with her now -- however messy it gets -- than when she is literally on her deathbed.

Jassy,
I am sorry you have been holding onto this hurt for so long. I am sorry for your sisters as well that they have found it necessary to be separated from their family of origin. We can’t know the pains or sorrows or memories that drive people but we can focus on light, on happiness, on peace and aspire to not hold grudges, to not judge others, to understand that we can’t know another’s pain and motivation.

You are asking for advice. Mine would be to practice gratitude. Keep a journal. Find a therapist to help you recognize where you have opportunities to heal.

As this is a caregivers forum, I will also suggest that you care for yourself and recognize that mom is well and her relationships with her daughters are her own. Pace yourself and enjoy your life. You can only change you.

Any unresolved issues should be resolved before the death of any of the parties involved, so as not to continue to carry these issues going forward. The fact that you say that your mom is "doing well" perhaps it best that your siblings get together with your mom now before she is actually on her death bed, to address said issues, and get things off their chests, which can be very freeing and healing for all involved, including your mom.
You may need to suggest that to them.
I can only guess that you have made peace with the fact that you didn't have good parents(like many of us didn't) and have moved forward. Either that or you are still in denial. I hope the latter isn't true as you will have to sooner or later deal with the truth as well. And hopefully that will be before your mom passes.