Want to know the divorce law from widow?

You have not disclosed as to which personal Laws you belongs to? Any way most commonly I believe you to be a Hindu by religion and advise you on its basis.

See, after marrying a hindu woman ( Widow) you also adopt her minor children as of your's and under Hindu law the Maxim of "Once adopted ever adopted" prevails. Thus, you now can not deny the status of their being your sons or daughters. Rest the rights of a son or of a daughter are very much clear to all as per hIndu Law which are not to explain further to make a crisp and short answer of your enquiry. 

For any further clarifications you can call me on phone.

By marrying a divorced woman with two children, all of them have become your family members. The fact that the woman is demanding more money to meet her and family expenses cannot be a ground to divorce her. If she agrees both of you can file for divorce by mutual consent. But take care, you cannot escape your obligation to maintain the children and meet their educational and other expenses until they attain majority and start making their own living.

The posting suggests no specific cause of action for seeking divorce. 

You have married that widow or not ,not clear ,if Ur not married then u have live in relationship with her ,not clear ,her first husband's children's are only step children's to you until you adopt them ,so she cannot claim any maintenance on behalf of them ,they are only entitled to their biological  father's asset only ,deny marriage if she approached court.

File a petition for mutual consent divorce on justified ground(s), if any, which do not suggest any such ground in the facts posted by you.

What next have you planned after divorce from this (second) marriage ?