Now my question is that,
1. whether we ( Legal heirs of my mother- myself and my sisters) are also having any rights over such properties.
If the properties in question belonged to your deceased grandfather and if he was reported to have died intestate i.e., without making any arrangement for distribution of the same among his legal heirs, then the properties that stood on your grandfather shall devolve equally on all his legal heirs consisting his wife and children. thus your mother being a legal heir to your deceased grandfather, is entitled to an equal share in her father's properties.Since your mother is no more, her own legal heirs i.e., her children and husband are entitled to acquire and enjoy her share in that property as right of inheritance or intestate succession.
Therefore you along with your siblings and father can file a partition suit agaisnt all those who have taken away the properties without giving a share to your mother as her legal heirs, with prayer for separate possession.
If the amicable talks fail to fetch any fruitful results, then you may proceed as per law with a partition suit. There is no limitation for filing partition suit.
2. Whether such partition is legally correct or not. Because they (My mothers siblings) have not given any share to us.
This partition suit is legally valid and that is the only solution available before you for the present.