A mortgage loan or, simply, mortgage is used either by purchasers of real property to raise funds to buy real estate, or alternatively by existing property owners to raise funds for any purpose, while putting a lien on the property being mortgaged. The loan is "secured" on the borrower's property through a process known as mortgage origination. This means that a legal mechanism is put into place which allows the lender to take possession and sell the secured property ("foreclosure" or "repossession") to pay off the loan in the event the borrower defaults on the loan or otherwise fails to abide by its terms.
The simple answer is no, the wife has absolutely no financial obligations towards her husband, her in-laws, or anybody else.
Anything she gives, she gives out of her good will and good akhlaq. She has the option of being generous and contributing, if she is capable of doing so, and willing, and she has the option of not, as that is completely up to her.
The husband or his family have no right forcing her or persuading her to contribute, and she needs to be careful to know her rights. If she is contributing to the mortgage, then she has an option of being a part of the legal ownership of the property, and so on...
With prayers for your success.
She must be careful that she is not being mistreated or manipulated in
Yes, it is allowed if it is necessary.
Yes, it is permissible to buy a house on mortgage from a non Muslim bank.
This is according to the most learned scholars who are known as Maraaji' of Taqleed.