Is it legal or illegal to marry two girls in India? it is right or wrong?

Legally you can't marry two girls if you are a Hindu or Christian. But if you are a Muslim you can have more the one living wife.
But there are instances where people married more than one girl. If the wife gives in writing that she has no objection to her husband marrying another girl. This consent should be given by her in presence of a lawyer and the statement should be notarized. If she gives her consent also you should not marry another girl. She may go to court and say that you made her sign on the paper by threatening her. So normal declaration is not Ok. It should be notarised. In such case she complains also court will be in your favour only. Similarly, a girl also can't marry two boys without the consent of her husband. Anybody violating this can be imprisoned for up to 7 years and a fine may also be imposed. This is as per the Section 494 of the Indian Penal Code, 1908.
If nobody gives any complaint one can have two wives or two husbands and no court will punish. But if somebody gives a complaint the courts will come into the picture.

If you belong to Hindu Community, you cannot marry two girls legally. The same thing holds good for the the Christians. However, being a Muslim, they have the privilege of marrying as many girls as they want since their religion does not have any objection in this regard.
However, in some exceptional circumstances, a man can contract marriage with another girl in the Hindu Community despite having a wife in some exceptional circumstances. This could be due to her inability to conceive and from the side of the husband and his close relatives, there is a pressure for a fresh marriage of the husband with some girl, the marriage can be negotiated with the consent of his first wife. The same has to be approved from the court even,
However, being a Hindu or a Christian and are on the job in a government service or a public undertaking, an employee should have a single wife and in case of noncompliance of the same, one is liable to be punished.

It is illegal to marry two girls in Hindu and Christian communities. But, in the Muslim community, it is allowed. In the olden days, having more than one wife was very much in practice and legally binding. Muslim people used to marry more than one girl freely. The laws prevailing at that time were not harsh or strict concerning polygamy. Thus, people used to practice polygamy without any fear of punishment. But, nowadays it is very risky because article 494 may be applicable for violating the rule in which up to 7 years imprisonment and fine are included. You can have more than one wife if your first wife gives a consent letter about no objection as written statement proof. Then only, you can consider having another girl. On the other hand, if she is against marrying another girl then you can't do it. If you do against her wishes then you may have to face a lot of problems in future.

Marrying many girls is indirectly happening daily in our country. The main thing is if any one of the wife is making complaint only it is coming to light and for adjudication.
One of my friend arranged for a marriage of his daughter, who educated in college level. Both my friend and his wife came to know after the marriage got fixed, betrothal was over only that she was having some affair with another auto driver, who already got married. By believing that was just infatuation and would be alright once the marriage was over, they continued the marriage arrangements by advising her to forget the affair. After the marriage was over the girl went to Bangalore as the bridegroom was working in Bangalore. Next day morning they reached Bangalore she removed her mangalsutra in the Bathroom with a note and eloped away. Much worried parents on both sides felt bad and my friend's wife got paralytic attack and admitted in an hospital. Without knowing what to do next, my friend got puzzled and left the girl without searching. Recently it is learned that the girl is living with that auto driver and his first family.
So the thinking of another marriage should not come into anybody's mind on any situation.

Polygamy and Polyandry( having more than one wife or having more than one husband respectively) were accepted and common in the olden times in different societies. From the ancient epics, classics and history books we understand that the same was practiced in our country also in olden times.

However for the sake of equity and smooth functioning of society with the availability of resources, laws and regulations are made in modern society. In the very recent times for the welfare of children and welfare and equality to women more laws are made by which polyandry or polygamy are discouraged or prohibited by law. However still a few nations and communities or societies practice them, but by and large society is now monogamous .
In our country India, polygamy or polyandry is not allowed freely and permitted under certain conditions (for people following particular religion),as allowed by the respective statutes and constitution. However for government employees and people holding certain positions this is not allowed as per their code of conduct and rules even if otherwise eligible to practice.

In Ramayana, Dasaratha, father of Lord Rama is said to have more than one wife. But Lord Rama has only one wife. So without giving any direct verdict Ramayana conveys the message by calling Dasaratha just an emperor, but Lord Rama as God's avatar.
The matter of remarriage by a widow or widower is different. At the time of the remarriage earlier spouse is not alive. So it is not polygamy or polyandry.

So before harboring any such thoughts of having two wives at the same time, please ensure that you are eligible for that as per the existing laws and statutes or code of conduct of employment. Even then, the woman should also comply with full consent and she also should be eligible to enter into such a marriage as per the prevalent laws and conditions.

As per Hindu marriage act it is illegal to marry with two girls. In some communities it is allowed due to religious reasons and they can exercise this right as per the traditions of their community but it should be a known fact and should not be challengeable in a court of law. For example a Muslim person can marry with more number of girls.
There are some legal processes by which people manage marrying with more number of girls like changing one's religion and things like that. But they also have their own complications especially in case of property disputes.
It is said that if the existing wife does not object then one can go for a second marriage but it is an internal understanding and arrangement of the family and does not have a legal sanctity.