Zoya Ji,
FIRST, make it clear that your Uncle need not pay the amount of six lakhs rupees.
Becasue in a Khula, a Muslim Man receives compensation for releasing his wife from marriage tie.
Khula is a Divorce with the consent and at the instance of the Wife.
In Khula a Husband is never liable to pay any compensation to his Wife.
But a Wife is liable to pay compensation to her Husband instead.
If in the Khula papers, your Uncle has agreed to pay the amount of six lakhs rupees to her, then such condition is not valid.
SECONDLY, a Divorced Muslim Woman is entitled to all the properties given to her before or at the time of marriage or after the marriage by her Husband.
[Section 3 (1) (d) of The Muslim Women (Protection of Rights on Divorce) Act, 1986]
Therefore, the properties given to her by your Uncle cannot be legally recovered.
THIRDLY, in any kind of Personal Law, a married woman cannot refuse to live at her Husband's home without reasonable excuse.
So, a married woman cannot force her Husband to live at place of her wish, because wherever the Husband lives is the matrimonial home for the wife.
Your Uncle's wife cannot force your Uncle to shift to her parents home/place.
And if she does do, without any reasonable excuse, it is wrong and also bad in law.
IN MY OPINION, your Uncle need not pay the amount of six lakhs to her.
But on the other hand, your uncle cannot recover money/gold etc. given to his wife before/during/after the marriage.
If there is a valid Khula, then your Uncle is entitled to compensation for it.
If they threatening to file cases, I think must be false, so your Uncle can defend such false cases.