Marrying one's ex-wife's daughter

Q: Is it possible to marry an ex-wife's daughter? I know a man that married a woman 13 years older and she never told him she has a daughter almost his age. They are not together any longer and he wants to propose to the daughter. Is this permissible considering he didn't know this? He didn't have intercourse with her since finding out as he was very hurt and shocked.

Getting a fixed return from an investment

Q: I give $5000 to a person in pakistan for investment. He told me that he will give me monthly $300/month on the top of that money. The condition is that the amount on top of $5000 can be $300 or more or less depending upon the business sales.

The second condition is that the owner told me that I can't give you guarantee for $5000 as incase if theres a loss then he will not be responsible for the loss.

My question is, is the $300/monthly return on the $5000  halal or haram?