How did you purchase this house? Has the sale deed been executed? Does the agreement/sale deed have any embargo on your right to construct an additional floor? If there is no such clause in it then it is your right to construct an additional floor. The decision to seek a stay order from the court against any attempt to stop you from constructing the additional floor is a wise decision.

You are under no obligation to give any donation for ganesha. Tell them to go ahead and file the complaint. Nobody can be forced to give a donation. You can lodge a counter complaint against them for threatening you.

1) I presume that you and your brother are absolute owners of land on which house is being constructed . if building plans are sanctioned by municipal corporation you can construct additional floor .

2) as far as complaints made by locals are concerned if there is no substance in complaint you have nothing to feat . if you have not encroached on common road don't worry .

3) as far as donation to ganesha mandal is concerned you should not bow down to black mail tactics . refuse to pay Rs 30,000 but as gesture of goodwill you can make such contribution as suits your budget .

make it clear that this is all you can afford and lodging complaint against you may not help them in recovering any money from you . handle situation tactfully . lodging police complaint will only aggravate the issue