AITAH for refusing to share the inheritance my old neighboor left me which was meant for her grand daughters?

This is all a mess and i'm a still a bit in desbelief for all that is happening because i really wasn't expecting it.

So since 6 years i changed country for a job promotion to the head quarters of my company. When i arrived i looked for a house in a nice neighborhood and when i finally found it in my first week there was this old sweet old lady which welcomed with home made cookies. Obviously during the first times i was super stressed with work since i wanted to prove my value and show that i deserved my promotion so i was honestly spending not so much time with neighboors and all this stuff. But the only constant was this sweet old lady that from time to time was shwoing up and just wanted some company so it wasn't a big deal for me. After a year of me finally establishing here i had more and more time so i started to spent more time with my neighboor too.

During the years i learned that her husband died 20 years ago, that he left her the house and some money but whenever i asked her if she had any grand kid she would become sad so i would just drop it. Obviously during the years she opened more and more and i learnt that she had 3 grand daughters that were living at 20 minutes from her but she didn't saw them since 13 years and they never made any effort to come visit her and this was clearly extremely painful for her since she didn't understood why and all she wanted was just some company and to see them from to time. I have to clarify that i didn't knew anything about her financial situation since she never talked to me about it and honestly i never cared because like i said when i got promoted here it came with an extremely important raise too so to me money were never an issue and i'm not for sure some type of gold digger since i'm well of with money.

During the years we became more and more close by simple stuff. Like helping her out with her garden, she teached me some of her recipes and she officially become simply part of my life. I even invited her with my family some times during the holidays because it was hurting me to see her always alone. And to me we developed this close relathionship since i saw in her a bit my grandma that i knew only for a few years because she died for heart problems. And the thing that hurted me just like she said was that in this 6 years not once her grand daughters showed up for her or just called her. Simply nothing so i tried my best to spend time with her and make her feel less alone.

Skip forward to 3 months ago and unfortunetly she died from complications due to her age and health problems. ( S, her name, was 96 when she died)

But again at her funeral literally no one of her family showed up. It was kinda absurd that i was there with her old friends and her family didn't even bothered.

And here comes the issue. 2 weeks after her death i was contacted by her lawyer for her will, which obviously surprised me, and i found out that she left me her house and all her money. In her will stated that she thought a lot about what she had and decided to give everything to me with the hope i would keep her house for when i would have kids and give the money to a charity organization for cancer research. (Like i said she knew that money wasn't a problem for me)

And here is the all mess because suddenly her grand daughters remembered about her and their first move? To contest her will obviously because according to them i manipulated S into this and when she changed her will she clearly wasn't thinking straight. Useless to say that it was useless and i found out that she changed her will 2 years ago so well before her death and that everything is perfectly legal and she was in perfect mental health when she changed her will.

Apparently this only made things worst and the grand daughters started accusing me that i somehow manipulated S into this and i admit that i got extremely angry with them because i pointed out how no one of them was there for S in this 6 years and before, how no one of them was even at her funeral and that they should be ashamed of themselves for leaving their grandma alone for almost 20 years without ever showing up or even calling her once.

And the reason why they are so angry and so aggressive is because the money S left me aren't exactly small and the value of the house is extremely important since we live in an extremely good neighborhood.

I obviously want to honor her wish and to donate the money at the charity organization S mentioned.

So AITAH for refusing to give the inheritance to them? Should i share it at least or should i just respect S's wish?