The word, asbestos, scares a lot of folks mostly through ignorance. To reinforce a big difference in the composition of asbestos products, there are friable and non-friable asbestos products. The friable ones can become airborne simply by handling it. The non-friable asbestos products will only become airborne if it's able to be 'reduced' to a powder. In asbestos siding, generally about 1% of it is made up of asbestos and in this form, it's of the non-friable variety. If you crush it, drop it, pound it with a hammer, you expose that 1% to the air. Hence, the danger. Again, it's through ignorance. If the homeowner is aware of the handling and disposal regulation, like myself (in my area), it's not a problem. I know how to handle it and properly dispose of it. BUT, I would tell you that if I was looking at a home to buy, I'd want to take a peak underneath the siding. I don't care how new the home is. Also, as a general rule, I'd want the seller to sign a disclosure form. Why? Because buyer beware. The seller disclosure requires they 'tall all' to the best of their ability. One may sue if one finds that the forms says 'no asbestos' and there actually is. BUT one may not necessarily win. Why? Because the new owner has to prove that the previous owner knew it. Remember, (in my area), there are no federal, state, or local laws governing the removal and disposal of asbestos cement shingles in owner-occupied single family dwellings. (Rentals + multi-family dwellings have regulations). Should the federal, state, or local laws change regarding its removal and disposal, you may have to disclose and bye-bye (from my perspective) potential home buyer. Once they become educated AND there are laws in place, there will be new headaches for sellers and buyers.
Right now, I can't say anything about the laws in your state or local. Unless the asbestos siding is regulated (check your municipality and state EPA), I don't see why you have to disclose. There are no real health hazards with living in a home that has asbestos cement siding. Again, the danger is when you are handling it, removing it, dropping it, etc., etc.. What I, personally, think is this ... When you go to sell the home, tell the realtor to ASK the potential buyer why they DON'T want to buy the home. DON'T say ANYTHING to the agent that you're looking for info about the siding. Maybe you can 'worm' the question to say something like, "Why, don't they like the color of the siding or somethin'???" This may 'draw' some attention to the agent to recall if he/she heard anything about the siding. (Plus, in asking the agent the 'why' question, you may learn about people's tastes in home buying. This is a good thing from a seller's perspective anyway. Moving right along ...) Assuming you hear directly that the asbestos is a problem with the potential buyer, WORK with the agent AND the buyer to see if you can come to an agreement. Maybe you can get estimates on a siding job and split that cost. If it's gonna cost $8500, take $4250 off the price of the home. It's that simple. The buyer feels like they're getting something and you sell your home and count your blessings. If I figure right, this amout of $$$ isn't going to hurt the pockets of your Grandparents assuming they've been in the home for 'scores' of years. You can't be greedy. At one time, this type of siding was the way to go. Today, things are different. So, too, must your 'views' in matters such as these.
Best to ya (and your Grandparents). If you need more info, e-mail me directly.