Nikaah & Marriage Issues

Masturbation

Q: Scholars who don't allow masturbation as adopting lesser of the two evils like to avoid zina when there is real fear, do these scholars consider masturbation and zina equal in sin, when only done to avoid zina. What's their stance like many Maliki scholars and Shafi?

Secret nikaah

Q: I am married and a widow who  has children of his own wants to make Nikah with me, but we both want to keep it secret (although in Islam nikah should be notified to family and friends) but in our current circumstances it is very hard. She says that she does not require anything from but to fulfill her sexual desires. We both agree on this that it will remain a secret and will not affect both families at any level. 

As her children are elders and she said that her children will not accept my decision and hate will grow if she declares nikah. So as husband I will fulfill her nan-nafqa although she is repeatedly denying as she is earning so she said she won't require anything. 

The main purpose for this nikah is to avoid sin. So what should we do as a declaration will lead to unpleasant results from both families. 

Please guide in all possible scenerios.

Marrying one's foster aunt

Q: There's a girl and we like each other. Finally we decided to get married. 

The question is, she's a sister of my aunty (chachi) (my father's brother wife) and my aunty (chachi) is my foster mother as she fed me breast milk two times only while I was 18 months old. 

So am I allowed to get married to her sister or not?