Is it permissible for a person to give the Zakah (obligatory charity) to his daughter-in-law?

Yes, it is permissible for a person to give the Zakah to his daughter-in-law if she was poor, and none provided for particularly by whom are obliged to provide for her. And Allah Knows Best.

Is it permissible for us to sever ties of kinship if our blood-relatives` gatherings/meetings involve acts of sin?

Observing kinship ties is obligatory, and paying your blood-relatives a visit causing their sinful acts to be hindered , then you should do so. However, if their sinful acts continue while you are at their gathering and they didn't respond positively, then observing kinship ties via telephone and the like will suffice in this case. And Allah Knows 

Is it permissible for someone who has forgotten to mention the supplication pertaining to answering the call of nature to say it while in the toilet?

It is disliked for a Muslim to mention Allah while in the toilet, but he/she may recall the supplication in his/her head without uttering it; that is in case he/she had forgotten mentioning it before entering the toilet.

I am pregnant with four twins since two months although I didn't have childbearing potential during the last four years. In addition, the doctor specialized in reprusccusions, already has notified me about the possible reprusccusions as a result of being pregnant with four twins as follows: abortion, Metrorrhagia, Premature birth, high blood pressure, gestational diabetes and the like. What is the ruling on aborting some of the aforementioned embryos? A medical report was attached in which the status of my question is clarified.