Making Allah Ta'ala a witness in a nikaah

Q: While getting married to someone you need at least two witnesses one male and two females or two males and one female. What if someone gets married in secret without telling anyone and they make Allah their witness and say qabul?

I read somewhere that if a mature girl and boy says qabul with the intention of making her/him their spouses, they'll eventually become husband and wife in the eyes of Allah. Is it true?

One of my cousins secretly went into a relationship and she considers that guy as her husband. He also considers her as his wife. So with a pure heart are they married in the eyes of Allah?

Working online under someone else's name and profile

Q: My sister recently applied for a tutoring job with good payment online. However, due to being occupied with household chores, she asked me to tutor the kids under her name and profile (without the one who hired knowing) since I am looking for a tutoring online job too. I'm not as qualified as her although I'm qualified enough to tutor those kids but I refused thinking that it would be a deception. Was this act permissible?

Father discharging sadaqatul fitr on behalf of his baaligh children

Q: Will sadaqatul fitr be discharged if the father discharged it on behalf of his baaligh children (who have above the nisaab amount but he still looks after them) but they were only informed that the sadaqatul fitr was discharged in their behalf a few days after Ramadan ended. He pays their sadaqatul fitr every year but forgot to actually mention it to them this year before discharging it.