How can we deal with this so she won't complain against my dad and defame him?
This is just common odmestic problem and it is better to keep away from her and don' argue with her.Ignore
Can my dad also file a complaint under men cell?
There is no men cell so far, however he can file simple police complaint for threats he receive.
How can we prevent the assets going to her brother?
If the property belongs to your mother and that is in her own name then she can gift or sell or give that to anyone she desieres. You can only win her heart by making her happy to get the property . Legally you cannot force her to transfer the property in your names.
Is it possible?
No, legally not possioble. However you can file a suit disputing title and all that , that may fetch a stay but that too would vacate one day having no legality.
Can she donate the shared self acquired properties to her brother without my dad's consent?
Yes very much ,it is her property her owned property, she has all the rights to do whatever she wills.
Can I object this as an anticipatory measure?
No, as i said before you can file suit and stay the transfer for sometime but that will not run longer and will finally get dismissed may be that will take yaers to decide, but she can make a will and will transfer her peoprty in anyone's name
I'm so frustrated that she doesn't have a moral respect for her family Though I'm married, don't I have the rights to get the assets under Hindu Law though I'm a daughter?
No , as the property belongs to your mother and that is her owned property untill she is alive you can do nothing. If in her life time she gifts or transfers the property to anyone esle you can do nothing. Even she can make a will and the property will be distributed/transferred according to her will.