Addressing invites

am sitting here typing up the addresses for the formal and informal envelopes and need some advice please
1) For the informal FI and i are chose to do everyones first names
ex. Bob and Donna
Does the women or mans name go first? and childrens names go on the next line

2) do you spell out apartment and does it go on the same line as the address
ex: 123 Oldmill Road Apartment 2
or
123 Oldmill Road, Apartment 2 (with the comma)
or
123 Oldmill Road
Apartment 2
Blah blah, New York 12345

3) does it sound stupid when i write on the inner envelope Debbie and guest
I really dont want to write Miss. Debbie and guest (too formal for me i think)

4) if 2 women live at the same address (widowed and sisters) can I write:
Ms. Ann Blah and Ms. Britney Blah
or are thier names one under another?


Sorry so long! Thanks guys :)