This appears to be a typical case of greed of the daughter or more probably that of the son-in-law. How on earth 498A can be applied in this case? 498A deals with husband treating the wife with cruelty. Where is violence here? Under the first explanation is her mother in danger of committing suicide? The second explanation is violence with respect to demand for property. Who is demanding what property? A wife demanding property from husband or his relatives is not intended here. The lady here is giving a new dimension to the misuse of 498A.
The problem here may be because the donee, the son here, is married. It is universal that a mother-in-law feels that a daughter-in-law is an intruder from outside, who claims rights on things, particulaly a property like a dwelling, which should legitimately belong to her (the mother-in-law). Her daughter then makes common cause with her mother and acts ostensibly to rescue the mother. I have seen such things happening after the death of a testator. Most probably here the father has wisely transferred his property to his son, during his life-time itself. In case of any dispute he will be there to defend his actions. Having property or income, though important, that alone will not protect an old parent in his or her old age. There should be a son or a daughter to look after them, to fulfill their personal needs, cooking food included, to take them to doctor if they fall sick or have any ailments, to take them to hospital and attend on them there and so many other things. The father here believes that his son and daughter-in-law will look after their mother after his death. Also even if his daughter-in-law cannot be trusted, his son is not a joru ka ghulam.
I bring to the attention of the lady here or more importantly to her husband, the following sloka from Subhash*tam:
उत्तमो आत्मना ख्याता ख्याता पितरेण मध्यमा
मातुलेनधमाख्याता श्वशुरेणधमाधमा
One who achieves prestige on his own is the greatest. The one who achieves greatness through father is average. Achieving greatness through maternal uncle is bad enough. But to aspire for greatness through father-in-law is worse than the worst.
So if possible be a loving sister to your brother and a loving daughter to your parents. If at all the worst happens, as your fear, you are there to take care of your mother. That would the best way to show affection to yor mother, rather than going to court as though you are doing it for your mother. You and your husbands are earning good salaries