If I understand correctly, the property standing in the name of your wife acquired out of HUF funds was gifted to her brother.
1 There is no capital gains in the hands of your wife or HUF at the time of the gift. The actual cost of acquisition of the property in the hands of the HUF will be the cost of acquisition in the hands of her brother, as and when he sells the property.
2 The gift may be disclosed in your IT returns as and when needed. As there is no receipt of consideration, there is no tax liability. Hence, there is no need to disclose the deletion of the HUF property in the IT Return. However, if you are filing any Wealth tax return, you will have to disclose the deletion.
Even in the Income Tax also, if you were offering rental income on such property, the rental income would no longer be yours. If you still continued to disclose the rental income, it is more like transfer of asset without transfer of the income, which is the reverse of the provisions relating to the transfer of income without transfer of the underlying asset.
You need to take proper legal opinion by scrutiny of documents executed and available with the sub-registrar.
3 I am not clear about your question. If I understand it correctly, the the date of possession in the hands of HUF and the date of possession in the hands of your wife's brother are the dates you are referring to. If its so, there is no tax liability, as there is no gift tax on the property gifted.
4 There is no tax liability at the time of gift.
5 The HUF and Coppareceners may individually proceed against your wife legally, if you wish to.
In the hands of your brother in law, the applicability of Section 56(2)(vi) or (vii) needs to be considered, as there is gift of the property.