a very difficult topic.
1.) you are afraid that someone will take "your" money away from you. that makes you no better than the uncle.
2.) the thing with changing the inheritance is kind of nonsense. if anything, one can challenge the deceased’s will and somehow have it declared invalid, but definitely not change it (after all, it is the last will and you cannot ask for changes).
3.) you are "deliberately" going there to dissuade grandma from changing the will. which again supports point 1.
4.) the relatives sit at grandma’s door every week. they "take care" of her, whatever that means. and if it means that they come on Sundays for coffee and quote "eat everything away from you" (which in turn only sounds like envy), but they are there. grandma is definitely happy about the visits. you only come by once and want to talk about her death right away.
and from the other side:
1.) very old people often do not change their will. one was made earlier when both were alive, one died, the other inherited everything. now the last surviving person usually does not care at all what happens afterward. a new will for old people is considered a high hurdle in their belief with a notary etc. plus, they have to deal with their own death.
2.) a gift or something similar has to be at least 10 years ago in order not to become part of the estate. with grandma being 97 years old, it is highly unlikely she will reach 108. so there is no need to worry about that.
3.) grandma could sell the house to the uncle or make an agreement that the uncle, for example, pays for the nursing home. however, he will not get away with paying 1,000€ per month for a year and then inheriting a house worth 500,000€.
4.) in case of emergency, a certificate of inheritance is issued. it clearly determines who will be the heirs. it is impossible to be bypassed there since the whole thing is done officially by the authorities. the process also costs a lot of money (a percentage of the estate).
5.) if the certificate of inheritance lists, for example, 4 heirs (e.g., 2 grandchildren and 2 children), each will be registered proportionally in the land register of the property. the sale of the property would be ONLY possible if ALL sign. so it is impossible to cheat you here. the purchase price is inevitably known to you since it is an essential part of the notarized contract.
6.) usually all income from sales is deposited into the deceased’s account. because the account itself is also part of the estate (whether it has a plus or minus balance...), and then the heirs meet at the bank to arrange the payout and closure of the account. for this, the certificate of inheritance is required so the bank knows who gets how much.
7.) as long as the house is not sold, costs arise for it. these are usually paid from the deceased’s account if there is a certificate of inheritance (before that, the account is normally blocked). usually one heir will take care of the matters so that things move forward. he mostly has access to the account and can pay bills or commission someone to do something on the house (e.g., keep the garden area nice, otherwise no one will buy it). if someone messes up here, the bank staff will see that and will of course adjust the payout accordingly in the end. the person should get a certain "fee" though, as he has a lot of work...
I have gone through the whole story with my aunt, who never cared about my grandparents. in the end, everything depends on being able to solve it peacefully anyway.