Questions about 3 recommendation letters

I have below questions about recommendation letters I am planning to include and the dilemma I think if someone can guide me.

Letter (1): From a reputed machine learning trainer working in a Big tech company. He sent me recommendation letter as he liked my open-source work.
** + Challenge:** He sent me this as an email and not on company letterhead document, from his official email address which has his phone number at the end. He addressed this email to TechNation UK. Second challenge is that he knows me through my open-source work and not by working directly as colleagues. Will this work?

Letter (2): From an startup founder and CEO, who is chairman of the official blockchain association in his country. He knows me through my mentoring and helping him create a sentiment analysis AI model which I did as voluntary unpaid work, while working full time in another job. I met him on an online forum for AI which I moderate and work as an admin of the group.

** + Challenge:** I didn’t work for him as an employee but as a volunteer and mentor. Will this be rejected by labeling this as freelance work? Although I didn’t get paid anything for the mentoring and AI work.

Letter (3): From a colleague I used to work with and he is working as a director AI in a UK based reputed company. He himself has been endorsed by Technation in the past.
** + Challenge:** None, I think this is one of the best letter from 3.

Letter 1, I think you can print the email if it is from his company email account. When you print it will show is official email. If he is a senior role is email signature will show he is qualified. Now i think the important part his how well he is able to speak about your work Your recommendation letters should be written by other people who know your work, not your immediate employers. I would focus more on if the person is considered a leader in tech, the strengthen of the recommendation and how long he/she knows you. Did he attached is cv? You need to add his cv or some other recognised profile. then add a note on another page to explain he is not allowed to use company letterhead.

**Letter (2): You don’t have to be an employee. Ensure they know you for up to a year.
Key things for the recommendation ;letters:

  • Be a senior member of their organisation
  • Know your work

Each letter must:

  • Be about your Global Talent application - you cannot use a letter that was written for another reason
  • Say how the person knows you
  • Show your achievements in the digital technology sector, and how you are a leader or potential leader
  • Say how you would benefit from living in the UK
  • Say how you would contribute to the digital technology field in the UK
  • Explain what plans you have for work in the future

This is very helpful, especially the advice that note on another page to explain he is not allowed to use company letterhead.

For letter 1,He is not in leadership role, but working as individual contributor. I was wondering if seniority can be compensated by his role as a machine learning trainer inside a big tech for internal employees and clients. As it requires much subject matter expertise to teach ML in such a company.

Much appreciate your valuable advice, not only for my question but for the community as a whole.

He is willing to send me his resume. For letter 1