your intentions are noble.......however, instead of house, you can perhaps just increase the amount of cash meher. since you dont intend to desert her like her sister's husband, you should hav confidence in your own stand, and not give in to any hard-coded demands. What if she turns out like what her sisters husband turned out like?
i know cases where girls married just for the meher/jewellery, adn then got a divorce within days of the marriage, on one pretext or another.
so its noble of u to understand her protecting herself, but you have to protect urself too. so find a common ground. yes letting parents handle it is a good option