"After the death of my wife, the said immovable property shall be inherited by my two sons in equal shares, AFTER the payment of Rs. 10,000/- to each of my daughters Latha, Vasavi, Chitra and Meera. "
So according to the will, things that stand out:
The will is very specific about who gets the house. You do not get any part of it the way it is written and the intentions behind it. You may be able to claim that since it was before 2004 when only males inherited property if the father dies without a will, that your dad decided to go along with the laws, but this argument would be a stretch. Your father from the way the will is written was an educated man who knew what he wanted for reasons only he knows. Perhaps in his mind, your brothers would be responsible for taking care of your mom after his death, or they may have helped with his business if he had one so that in his mind the boys contributed more to the parents and family wile the girls got married and were playing a bigger part in their new families. Regardless, his wishes are his wishes, and there may be little you can do to invalidate the will.
You may be able to also contest it on technical grounds but you will have to consult an experienced advocate on this. You may be able to contest on the grounds that your father bequeathed the house to your mother. In essence he gifted your mother the house. Normally when you gift someone with anything you lose the right to tell them person receiving the gift what to do with the gift once it is out of their possession. In which case it is a defective will and therefore invalid. Similarly if your mother did not make a will once the house was in her possession, then you can contest on the grounds that the house belonged to your mother after your father's death and if she died without making a will, then all of her heirs get a share as accorded by the Hindu succession act, assuming you are Hindu.
Now in the above phrase I copied from the will, it states that the boys inherit the house only AFTER they have paid you girls the 10,000 rupees each. So basically they cannot claim the house or sell it unless they have paid you your monies. So you CAN contest on that basis.
The 5 year period when did it start? Your mom died after your dad but when? The five year period starts from the date of her death. The date is crucial in determining whether you get more than 10,000.
Whether you can negotiate for more than 10,000 depends on whether it has been more than 5 years since your mother's death. If it is more than 5 yrs than you may have grounds to argue for more money from the end of five years to present based on cost of living and inflationary rate but more so as interest on the monies that should have been paid to you within 5 years. What would have been the interest charged if you went to get a personal loan from the bank, that would be the rate at which they would be paying. Since the will did not specifically state the monies should come from the proceeds of the sale of the house , you will not gain by contesting it on that ground.
Overall, you may have grounds to contest on technicalities, and you may have grounds on the fact that it is an unfair division of assets. However, the final decision will depend on the judge. Some judges may ask you all to compromise and settle your differences or you can do it yourselves without forking out money to pay lawyers and getting entangled in the Indian legal system for years and years.
You and your sisters have to decide what you would be happy with... A full share in the house or 1 upon rupees each. If you all get along, then have a family conference and see if you can convince your brothers that in the long run giving 5 lakes to their sisters isevetter than strangers getting a Whole lot more in the Way of lawyers fees, stamp fees, and every other kind of fee you can imagine never mind the bad blood it can create not only between siblings but also your children too and so on.
Please note the above is just my opinion, I am not a lawyer, but, I believe I know enough about wills dealing with my own father's will issues, that I feel fairly comfortable with the advice I have given.
I would urge you to consult a lawyer who is experienced in contesting wills.