[Vocabulary] letters - beginning with 'Dear ....'

[marker]

I'm wondering if it is natural to start a letter in the following ways:

Dear Mr Brown, ......................
Dear Mr John Brown, ..................... (name + surname - here I have doubts)

And what do we do when we write to two people?

Dear Mr John and Mary Brown, ....................
Dear Mr and Mrs Brown, ...................
Dear Mr Brown and Mrs Brown, ................

Thanks in advance for replies

 

[Grumpy]

I'm wondering if it is natural to start a letter in the following ways:

Dear Mr Brown, ......................
Dear Mr John Brown, ..................... (name + surname - here I have doubts)

And what do we do when we write to two people?

Dear Mr John and Mary Brown, ....................
Dear Mr and Mrs Brown, ...................
Dear Mr Brown and Mrs Brown, ................

Thanks in advance for replies

Those I have marked in red are the correct terms to use.

 

[marker]

Thank you for your reply Grumpy What do I do when I have to write an address in the same letter? I know I can use first names but I have no idea what to do with married couples

Mr John Brown (it's correct for sure)
23 Tall Street
........

Mr John Brown and Mrs Mary Brown (here I have doubts again because it seems too long)
23 Tall Street
........

Mr John and Mary Brown (sounds better, but is it correct?)
23 Tall Street
........

I'm waiting for suggestions again

 

[Rover_KE]

Mr J and Mrs M Brown.