@ Usha
At the very outset, I am sorry to hear about your situation. With the demise of your husband and a one year old child, no one should subject you to anything more but in fact should be supportive and help you rehabilitate.
Analysis of your situation.
1. You are a Indian citizen ( assumption-1) working in USA. Your minor child is in India with your parents. Your son is a Indian citizen and holds a Indian passport ( assumption-2)
2. Your SIL is in USA and they are harassing you for your late husbands money.
3. The in-laws, grand parents have expressed desire to maintain contact with your son
4. Your in-laws MIL and FIL are in India (assumption-3) are harassing your son and your parents.
My take
1. You can apply for ex-parte DV orders to restain the SIL who is in USA to stop harassment. You will get the orders the same day. Orders are valid for 3 days until hearing. On hearing, you bring the emails and other evidence and you will be granted a domestic violence restraining order for anything from 1-3 years. DV filing, serving is all free.
Keep in mind that a DV will impact the employment of your SIL in the USA and it will most certainly affect their right to visitation with your son.
2. If you are in any one of the following states, then you can file the DV papers using this tool https://www.icandocs.org/
California,Georgia,Minnesota,Massachusetts,North Carolina,Oklahoma,Virginia
3. As the Indian advocates have suggested, you can get a protective order in India against your MIL to stop harassing your parents and your son.
4. If you are not a US citizen, then the fact that there is a DV protection may assist you in getting expedited Green Card, free / subsidized accomodation and many more monetary and other benefits.
Warning note for you
Since you are the sole legal guardian ( your parents are not legal guardians), if your DV hearing has any element of suspicion that you are not a good parent, then odds are against you and you could lose the child to the US government - that the child is located in India will not matter if the child is US citizen. Court will order the child to be brought bact into the US.
Second, if you decide not to file DV against your inlaws and the in-laws make a child visitation motion to the court and in that motion if they sling mud on you, you could potentially run into some serious issues and you could lose your child. On the contrary, if you are sling mud on them, then the court will give the SIL/MIL what is called as "Supervised visitation". The inlaws will have to pay money to a third party to meet the child for one to two hours. Current rate is $30-40 per hour to see own child under supervision. There is a more dirtier form if you want to make it real dirty and that is called as "clinically supervisied visitation". In this order, the other party/in laws/grand parents will have to pay a third party $100-$200 per hour.
As a counter-offensive strategy, you should immidiately file a stipulation in the US and Indian courts signed between you and your parents that in the event of any unfortunate event, the legal guardians will be your parents. This will prevent the US government from taking over your child.
As the real Sam has suggested, you should appear civil and give equal oppurtunity for grand parents of both sides to have relationship with the child. If the court feels that you are denying contact for the SIL, MIL with the child, you have serious consequences to face.
Please email me offline and we can chat : reachadamkumar@gmail.com
When you reply, first please state the citizenship status of your child, yourself, your in-laws, SIL.