Here is my analysis of what is happening....
The lawyer must have called up Bani and told her about Ranveer's plot against Jai. I am sure that the function night wasn't the first night that Ranveer was meeting the lawyer.
So, when Bani found out about this, the only way to save Jai's hard earned money was to claim 50% of his wealth. That way Ranveer won't be able to touch the wealth without Bani's approval.
Let me know what you think.
RIYA