Your father in law transferred the immovable property on his own volition and he had done it by executing a registered settlement deed in favor of your husband.
Your father in law's rights in the property have been alienated and he has no rights in the property to which he was holding the title until now hereafter.
Since your husband accepted the settlement deed by taking possession and had transferred all the records to his name, he becomes an absolute owner of the property with marketable title on his name.
Once your husband has marketable title to the property he can alienate or transfer or encumber the property in any manner or mode to any person of his choice or desire.
Nobody can interfere with the above rights of your husband.
Therefore the proposed registered settlement deed o be executed by your husband in your favor cannot be disputed by anyone on any grounds and if anyone does it , the same will not be maintainable in law.
Your father in law cannot cancel the settlement deed unilaterally as per his whims and fancies, it ill be invalid and unlawful.
Your husband can challenge any such move before the court of law.,