No, just no. Why would you consider putting your child into that environment with those parents? You tell her one time, then you refuse to discuss it further. Don't respond at all. She's harrassing you because it works and she thrives on the drama, which you are allowing yourself to be drawn into. Boundaries.

She's using the threat of suicide as emotional manipulation. Try and feel sorry for her as this is nothing more than a desperate attempt at control when she can't manage her emotions. She is unlikely to ever act on this threat but she definately needs help. This is actually your father's role but he would need to assert himself. In the US, a threat of suicide means an automatic 72 hour hold for a mental health assessment. Not sure about where you are but you might try asking her open ended questions next time she threatens. Suggest that since her threat is so alarming that you need to take her for emergency help and assessment. In other words, call her bluff but in a helpful way. Playing therapist is beyond your pay grade and you cannot help beyond support for seeking treatment for her. Continue to live your life and put strict boundaries on how much you will involve yourself.

No it's not typical and it's a huge red flag. Do not marry him unless this is sorted out- it will not get better. There is nothing you can do to help except support him in seeking professional help. First, an honest conversation with his doctor and a thorough exam to check for physical issues. Could be hormonal, thyroid etc. Then he needs a therapist to sort this out. This is reddit so I can't make any conclusions. Could be anything from hormonal issues, to trauma, or he's uncertain about his sexual orientation. If he values your relationship he will seek help.