Ancestoral & inherited property distribution

My dad & mom have togather made a will and divided two properties among myself & my sister 1, The house with land of 1 acre in my name: this land was given to my mom by her dad (moms ancestoral property) & my dad bought half of this land in his name and built the house in it so the whole one acre is - house and half land in my dads name acquired property & half my moms. 2. my dad sold his ancestoral properties and purchased a 2acre land in his name. This he has written in the WILL for my sister. To avoid dispute later on he wrote two separate docs & mentioned in each that the other person have no claim on the property. Now my questions are: Can my sister keep her share given & claim for a share of my land mentioning that its our mothers ancestoral property and she has a share in it too?? My mother is having a slight mental disorder & undergoing treatment for past 20yrs. But she has a stable mind & has gone with my dad to sign the will and is well aware of it...Can they make the above claim showing my mom's mental illness? If i transfer the properties written in the will in my name when my parents are alive(both of them are asking me to do so) will my sis be able to trouble later on?? please advice.