Archana can claim her maintenance and maintenance for child through domestic violence Act. She will get the same as the property is acquired through income from joint business

Law is that if the property is ancestral then your sister can lawfully claim her husband's share in the property and consequently the will shall be void. 

If it is self earned property then the existing will shall prevail and your sister shall not have any right to the property.

If the property is put into joint family property or it is purchased by fund of joint family then all members of joint family shall have equal right to the property and consequently the will shall be void to that extent. 

Archana has no share in joint family properties 

2) it is not ancestral property and father in law could have by will bequeathed it whom so ever he pleased 

Dear,

         Archana only claim share in ancestral property, not in this case.

         will is binding on all the members.

         Archana only claim in self earned property of her husband. 

1. See for the the self acquired properties the will is valid as the father is absolute owner of the property and he can transfer same on his wish.

2.See if the properties are joint income she can stake claim and can try before the court to contest same. 

1. Late Suresh Sakhare's Will is perfectly legal

2. he is not bound to provide for the widow of his deceased son

3. by and under a Will, a person can bequeath to any person of his choice

4. it is not even necessary that the person has to make a bequest in favour of his legal heirs

5. if making a bequest in favour of legal heirs were necessary, then there would be no provision of making a Will itself

6. the legal heirs are entitled to the share of the deceased only if the deceased dies without leaving a Will

7. if he has left a Will and by it has excluded a certain legal heir, then it is totally upto him as to how he wishes to distribute his assets after his death among his legatees named in the Will. As before stated the legatees or beneficiaries need not compulsorily be legal heirs of the deceased person

8. i assume that Nitin died prior to Suresh and left behind his widow Archana. Thus, had Suresh not left any Will, Archana would be his class 1 legal heir u/s 8 of Hindu Succession Act being the widow of a predeceased son

9. Archana can challenge the Will only on the grounds that the Will is forged or fabricated or that it was made by Suresh under undue influence etc. All that she will have to prove in Court

10. She certainly cannot raise title issues in respect of the properties bequeathed by the Will. So if a certain property is mentioned by the testator as his self acquired property but in fact it is a joint family property, then such a dispute cannot be raised while preferring a challenge to a Will

11. for raising title disputes, Archana will have to file a separate suit in civil court

12. court will not entertain title disputes in probate proceedings which are taken out to prove the Will

13. to prove a Will the legatee or the executor named in the Will has only to prove 3 essential things - 

a. that the Will was signed by the testator

b. that the Will was attested by 2 witnesses who saw the testator sign the Will

c. that the testator made his Will in a sound and disposing state of mind

14. once above ingredients are proved, then it is for the claimant who challenges the Will to prove otherwise

daughter-in-law does not have a right over the property of the father-in-law, either ancestral or self-acquired. However, a daughter-in-law do have property rights over husband's property after his demise. 

a. Is Will left by Suresh Sakhare not allowing fair share to Archana legally tenable?
Answer: Yes he can only dispose of the property with respect to his self-acquired share. He cannot dispose of the ancestral property.
You must state, does family business mean HUF?

b. Is there any merit in Archana's claim over the joint properties?
Answer: On what basis is it joint property? Is there proof to show that payment was made by joint members? Is there a HUF Deed?

This is my response to you:
1. Has the Will been probated? Did your sister take objection then?
2. If she did, please mention details of the proceeding;
3. She can also file a suit in the civil court;
4. She can file a partition suit and stake her claim if established that Mr. Nitin had contributed from his own pocket;
5. Consult a local lawyer and take steps. 

Yes, whether properties purchased from income of joint family business or self acquired, it was opened by father and his brothers, NO right of children.

IF nitin had any stake in the company like share holding etc that on his intestate death, wife and child could have claim on it.

NO.

If it was HUF than she could have say in the peropty.

1. If the property bequeathed in the Will was the testator's own and absolute property then the Will cannot be disputed. 

2. She may file a partition suit claiming her deceased husband's share in it. 

yes will left by father in law not allowing any share to hus daughter in law is legal as the properties are considered as self acquired property father in law. 

She can claim the property only if she can prove that her husband was part of the joint business before his death and properties were purchased during his life time. 

1. As per the information mentioned in the present query, makes it clear that the property which has been mentioned in the Will was bought for my the income of the joint family business.
2. Now, if the same business was carried forward by the father in law from him ancestors then these property are also ancestral property.
3. Forget about father in law share to be given to who as he has right to give to anyone, but at the same time his elder son has notional share in the property being the legal decedent of his grandfather.
4. Out of that notional portion, Archana would have share along with her children if any.