property based inquiry

Unless there was a legally valid transfer deed in the name of your husband from his mother, he stands with same rights in between co-sharers/Class 1 legal heirs of his mother.

Is he the only Son to your Mother in Law?

No sir he has two brothers and 3 married sister

Its not known why your Husband purchased the property in the name of Mother instead of his own name when presumably he availed loan in his own name. Its also not known what was written in the sale deed as to the source of funds towards margin of loan while purchasing the property.

Is the loan still being paid? Who has been paying this loan? Again presumed to be paid by your Husband.

As per the details provided by you and presuming that your Mother in Law passed away without writing a Will as to this property,  primarily I can conclude that your husband stands on par with other children in sharing the property.

Since you inform that your Husband alone cobtributed for purchase of the property, you may explore the possibility of having a family meeting and convincing other siblings, with proof/s of money paid by Husband in repaying the loan,  to accept for a settlement/relinquishing deed in favour of your Husband. This shall attract stamp duty for registering. Try for amicable settlement.

Too many presumptions and hence I advise you to consult a local reliable Lawyer with full details and be guided.

The general legal position explained by the Expert is correct. Try to get a relinquishment deed from other sharers in favor of your husband and get it registered. The deed should also be filed with the Bank from which the loan has been obtained and ensure that your husband's name is recorded as the owner on the death of your mother-in-law.

All the siblings have equal share in the intestate property left behind by deceased (your mother in-law) as opined and advised by experts, I concur it. 

In the event of death of the owner of a property that is mortgaged, the instalments remain as liabilities with a charge on the property. A good mortgage deed should also forsee such events as death of the debtor before closure of the mortgage. The legal heirs will have to discharge the liabilities to get full ownership of the property.