Since there is no will made by your father and no will also not like to litigate the same in the court of law with no reason.
You are well of with the legality
Everyone holds 1/6th share in the property and thus everyone holds their legal right vested into it if not given No Objection Certificate one cannot waive anyone's right.
Law doesn't recognize waiving of right with no reason,
Yes everyone holds their 1/6th share so u can very well sell 5/6th share to the builder and if builders agrees to face the litigation and everything (what most builders do) you can sell off the property or the house
Once the whole house is sold sister will bring a civil suit against you and builder. Where you will not have any right over the property and builder will have to face the litigation and linger it further to the level of compromise
This is the only method I hope