Playwriting
I'm not sure if your original question was about how to format the play on the page or how to structure a play. There are lots of web pages that we can direct you to that address each of them.
As others have said, at this point the idea is to get it down on paper and not worry about how it looks. As to the rest of it, some playwrights I know just start writing dialog and see what the characters say to each other. Others outline everything. I'm kind of in the middle: Know the major plot points and the characters well then just let them talk. Somehow they automatically navigate the plot points I have come up with - sometimes in just a few pages.
Since the play is about your grandparents, you have a solid idea about the characters. But you need to know how each is different - how they talk, how they think, their sentence structure, how they view the world. They may be very similar today but when they met, they were likely very different.
The plot points I always (well - usually) have in mind before I start are:
Inciting Incident: What happened before the play starts that results in the subject of the play. For example, a woman has unprotected sex.
Point of Attack: Something happens at the very start of the play that changes the world of the play forever. For example, the woman finds out that she is pregnant.
Climax: The major question of the play is resolved in a major crisis. For example, the woman decides to have and raise the child herself.
The denouement: Demonstrate the new world incorporating the resolution reached at the climax.
Between the Point of Attack and the Climax there are a number of obstacles that the protagonist has to overcome. For example, the woman's boyfriend wants her to have an abortion, her mother wants her to put the baby up for adoption, her father wants her to get married and so on.
The obstacles come in many varieties but here are the big three: Other people, her own internal issues, and environmental (car breaks down on the way to the hospital).
One other suggestion while I'm on my soapbox: Keep the number of characters down. In a book, it's easy to have a large cast. Same for a movie. It doesn't work for a play for many reasons. Shoot for four characters, settle for six with a maximum of eight.
Keep the play to a single set if at all possible. Every time you have to stop the play to change a set you lose the audience and it will take you up to ten minutes to get them back into the play.
Don't be too detailed about all the other stuff. Tell them what room it is and how many exits there are (bathroom, front door, bedroom) and a few details on how the room is furnished and the costumes (wealthy, poor, 1900's or contemporary). There will be experts to design all the details when it is presented. Don't try to do their work - they'll be better at it than you can ever be.
Doug
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