So based on your post, you own house free and clear, it has family/sentimental attachments and as of right now, you wrote it into your will that your son gets it if you still own it at your death.
Aunt has not been approached at any time since you inherited about her living situation? You haven't actually asked her or spoken to her at all other than glossing over the fact that she still is living there?
I'm not sure why you haven't sat down with your aunt and asked her what her plans are. So set that up.
Holding onto a property just because it belonged to family but isn't really logical or practical. If it were a really cool/historic house or has the potential to live there yourselves (like a small lakefront vacation home that's been used by the family for generations), sure, maybe keep it, live there and pass it on to the kid... but the only real issue here is that this nondescript, very old-and-needs-extensive-remodelng house belonged to family, and you seem to have a mental block separating the fact that it is just a piece of property that isn't going to do anything for you at all based on what you've said so far. You are going to spend the next X years paying for things that break or need fixing up, all the taxes and the insurance and never see a dime in benefit. So nothing but paying out on your end, never getting anything out of it at all. You are acting as a custodian and will come out poorer than when you started.
So it's a big sentimental attachment money pit basically. Not an asset since you never intend to sell/rent.
And you are extremely cash/investment poor right now.
Sentimentality aside, it's a really poor idea to hang onto this house. If your son wants it, is he planning on living there himself? If so, let him do so and pay you rent/upkeep on HIS future investment. Let aunt continue to live there with him.
All signs point to selling this as soon as you can arrange it if this is a hot market. You likely could assist aunt in locating a nice reasonable apartment that works for her without the necessity of anyone else having to pay for maintenance. Hell, you could kick in on her rent if you want to thank her for caring for your mom all those years. The invested proceeds from the house sale would kick off more than enough to help with this, and you'd still be able to leave a legacy for your son in a form that he'd likely better appreciate and use.
No more insurance, tax, maintenance, worry over potentials. And it becomes an actual asset to YOU.
I have experience with this sort of thing. I come from a family of hoarders and everything was "you CAN'T get rid of this" and taught from an early age that things have an almost magical quality if anyone in our family ever owned/touched/looked funny at it... it's taken me years(decades) to unlock the actual value from material things and the way we're taught to imbue emotional attachments to them. Basically you should try to start thinking of how to best benefit YOU, and your family NOW. The house is a house. It's does not represent your love for your family. It's not a test or a responsibility to keep for future generations, again, unless we're talking something of great historical import... it is just a house, just land. It's lovely that your family owned it, but they wouldn't want you to sacrifice your contentment or burden you with it (if they were loving, good people). If your aunt isn't absolutely dead-set in living there forever, then you should do all you can to help her find someplace nice for her that she can afford, and sell that place and put the money to work bettering your life, and the future of your family.