By Writing letters, Plurals

I have some problems,they are the phrases about time: yet, today, so far, to date, up to now, recently, lately, up to these few days, this morning, now, up to present. what do they mean? Are some of them duration? Do some of them represent sometime/some time in the past? yet: 1.up to the...

How do you make "Last Will and Testament" plural? How about "Power of Attorney". As you can probably tell I work for an attorney and I don't want to sound ignorant when writing letters to people including more than one document. Any help would be greatly appriciated.

Are they completely the same between writing letters and letter writing? Do we normally write a heading in plural or singular e.g. Writing Letters or Writing a Letter? I think i post this in a wrong section. Anyway, hope any response from you. Regards,