how to address...?

i received a christmas letter from my japanese girlfriend's mother and i'd like to send one in reply. i wonder how should i address her? for example, she just writes at the beginning: "アドリアンへ"
should i do the same using her name+san? does that sound impolite? any recommendations?

also, i want to send a letter to a married couple of japanese elders i met during my stay in japan and from which i received enormous help. let's say their last name is "nakayama" but i want it to look as if i'm writing to both of them, not only one, so i guess i should not use "中山さんへ" but something different. would "中山家族へ" be all right? is there a proper way to address them?

thanks for your help!

Adrian,

For your girlfriend's mother, the safest way is to write "(her full name)様" at either the beginning of the letter (common modern style influenced by Western culture) or at the end of the letter just before your own name (traditional and proper Japanese style).

For the married couple, why not write "中山ご夫妻へ" or "中山(first name of husband)様、(first name of wife)様"

Uco,

thank you very much for clearing my doubts. Now i can finally send my letters.

Once again, thanks for the big help.

-Adrian-