What to do when husband and in laws harass and no financial support?

The fact provided by you reflects that your husband is in an adulterous relationship with another woman. Indian law treats adultery as an offence under Section 497 of the Indian Penal Code, punishable with imprisonment which can be extended for a period of 5 years. Section 497 of the Indian Penal Code, 1860 reads as under:

"Whoever has sexual intercourse with a person who is and whom he knows or has reason to believe to be the wife of another man without the consent or connivance of that man, such sexual intercourse not amounting to the offence of rape, is guilty of the offence of adultery."

In view of above, you have an option to make a criminal complaint against  your husband (by evoking the penal section 497 and 499 of the Indian Penal Code) before the appropriate criminal court in India.

Further, the divorce laws depend upon the religion of the person. Assuming you are Hindus, you will be governed by the Hindu Marriage Act. 

Section 13 of the Hindu Marriage Act provides the various grounds on which divorce can be sought by one of the parties to a marriage. It is as follows: 

Section 13(1) states that a petition may be presented by either the husband or the wife, for dissolution of marriage by a decree of divorce on the ground that the other party-

i. has, after the solemnization of the marriage, had voluntary, sexual intercourse with any person other than his or her spouse; or

a. has, after the solemnization of the marriage, treated the petitioner with cruelty; or

In view of aforesaid , you can file a divorce petition under Section 13 (1) (i) and Section 13 (1) (ia) on the grounds of adultery and cruelty ,and seek dissolution of marriage. It is pertinent to mention here, that  to prove adultery   is generally  very difficult, the onus of proof is usually on the petitioner and you need to have strong and cogent evidence to prove that he has committed adultery. 

The evidence stated in query will have to examined  to conclude whether they are strong and cogent evidence to prove adultery.

With respect to maintenance, to give maintenance to the wife is natural obligation of husband , so you can file an application under 125 Criminal procedure Code for maintenance.

Further, with respect to the custody of your children, if  your children are minor then you need to file a petition for the custody of the children. Section 6 of The Hindu Minority and Guardianship Act states that the ‘natural guardian of a Hindu minor, in respect of the minor’s person as well as in respect of the minor’s property …. in the case of a boy or unmarried girl is the father, and after him, the mother, provided that the custody of a minor who has not completed the age of five years shall ordinarily be with the mother. For appointment of declaration of any person as guardian, the court shall consider the welfare of minor. The welfare of the child is determined neither by the economic affluence nor a deep mental or emotional concern for the well being of the child. The answer depends on the balancing of all these factors and determining what is best for the child’s total well being.

The above mentioned procedure is one option. 

The other option available for you is to file Mutual Consent Divorce under Section 13 B of Hindu Marriage Act 1955. But this is only possible if your husband is willing to give you divorce. So you will have to enter in an MOU /agreement with your husband wherein you will have to specify the terms of your divorce such as alimony/maintenance and custody of your children. This process is faster and cost effective.