498a

@Nancy,
The allegations for filing 498A are:

i)My father-in-law demanded that I should give Rs 5lacs

dowry demand coupled with physical / mental cruelty is an offence under Section 498-A.  Mere demand of dowry is not an offence under this section.

ii)My father-in-law threatened that he would make my husband to go for second marriage(my husband is muslim and I'm hindu and we got married through special marriage act )

in your case, special marriage Act is applicable, which prohibits bigamy and hence, even though he is a muslim, without obtaining proper divorce from the competent court of law, he is not entitled to go for another marriage.  If he takes such risk, you can take appropriate action under bigtamy law and put him behind bars.  The other people, who will be conspirators in the bigamy also will be prosecuted.  If you want to prevent him from going to second marriage and you get whiff of his such attempt, you can approach the civil court and get interim stay against him for going to second marriage.  I want to make it clear that even though he is a muslim, as he has undergone marriage under special marriage Act, he cannot give divorce by way of talaq or go for another marriage till he getsproper divorce from competent court. 

iii)My husband and in-laws together would assemble in my sister-in- law's room and after coming out of the room they would insult me and threatened that if i don't give money my husband would desert me.

You have to decide that whether the threat is sufficient enough to put into the category of "mental harassment" and if so, you are entitled to proceed further under Section 498-A.

iv)They threatened me that if  I don't convert , they would take away my baby (1.5 yrs) from me

Yes.  This threat is undoubtedly mental harassment.  But it is upto you to take recourse of Section 498-A or not.  Because, once you resort to such action, there is bleak chance for restitution of harmonious matrimonial relationship.

 

I want to file the child maintenance , but  i don't know whether before divorce i can file or not .Also I'm working .through what procedure could I file for it.And if my husband does not respond then what should be done.If he doesn't come to my place , then what about the 498a or the child maintenance

you can file child maintenance case under Section 125 cr.p.c. or under DV Act.  The child's expenses  required to be shared by both of you.The court will decide the quantum of maintenance after taking his income and your income and child's needs and the style of living.  Once court order is passed he has to comply it or face the consequences.