Thanks all for the thoughtful advices.
This house will cost around $1.13 mm, she is trying to seize this opprtunity while the interest rate is low to buy this house. She will need help with down payment so she can qualify for a conforming loan, CA conforming is about $7xx,000.00. Which means that the down payment will be around $500,000. I think she can come up with about $300,000 from herself and her mom/dad. I may loan her $200,000 for additional down payment.
Her husband is a small contractor (remodel bath/kitchen) whose income fluctuates and my niece earns about $105,000/yr. The husband's income can fluctuate between $40,000 to $80,000, they have one boy. Recently the parents of the husband gifted them a house worth around $600,000-$650,000. The husband's parents do not want them to sell the house unless it is absolutely necessary. The parents asked them to try for couple of years, and if they can't handle the payments then sell the house to reduce the loan (refi down the principal).
I think they are stretching themselves thin for this situation without selling the house. They are trying to buy a house in this city because of the excellent schools, the boy is three years old.
I do have the financial resouce to buy the hosue out right if needed but I do not want to do so. I am not worry too much about my niece flaking out as she is quite a responsible person. Her husband seems to be nice but I do not know him that well and that is the only concern.
My wife and I do not have children and eventually our estate will be passed on to my niece, nephew, and my wife's nices and nephews.
I do not like this situation one bit but she is my brother's daughter.
As for not gifting the money to my niece out right, I am not willing to do it at this point, she will inherit part of my estate when I die.
She also wants me to be on the title, kind of portecting her interest just in case, so it may look like I own 50% and her husband and herself own 50%.
She is ready to make an offer on a house today and I will be signing an offer with her.