Under the given situation, it is pathetic that you being just children of your father cannot claim any right over your father's share in the property during his lifetime.
If you are an unmarried daughter to your father then you can seek maintenance from your father, besides your mother can seek maintenance from your father under section 125 cr.p.c..
Your mother can file an injunction suit to restrain the the defendants from alienating your father's share in the property for creating charge over it for the sake of paying maintenance amount since your father neglected to maintain his wife and unmarried daughters.
No doubt how far this may be effective and maintainable, but this will certainly stir the hornet's nest.
Once all those people are dragged to court in one or the other case, they may come down for negotiations and settlement which will be a situation benefit to you.
Try one or the other strategy when you are not able to move legally.