Hi Victor,
These are interesting questions, thanks for thinking of me re: some of the poems from Domain. 
One of the first things that comes to mind are words from Margaret Avison (a big influence for me) in the Foreword to Always Now (first volume of her Collected Poems). Avison tells of her grade nine teacher and leader of the poetry club, Gladys Story, who gave her this piece of advice: “For the next ten years do not use the first person in any poem you write.” Clearly this had a huge impact on Avison’s early work, for example in poems like “The Swimmer’s Moment”, “Tennis” and “Snow”. Elizabeth Bishop (another big influence) also writes in many poems with a detachment, often a “we” instead of an “I” and achieves a tone that somehow transcends individual personal experience that I greatly admire. I can’t remember exactly, but I think my discovery of these two writers happened after the publication of Domain.
In my work in the last several years (since Domain), I’ve definitely been aiming for a more oblique approach to personal material—I’ve attached a poem, “Postcard from Bonaire” as an example. (It’s already been published in a journal, so as long as it’s credited, I don’t think there should be a problem if you want to use it on your website, etc. Certainly you can read it in the workshop!)
But even with the poems in Domain, my background to all of the material was the writers’ workshop motto: “If the poem’s speaker is an ‘I’, that ‘I’ is not necessarily the author of the poem.” In all of my workshops, whether I’m a participant or an instructor, one of the ground rules is that we refer to “the poem’s speaker” and not to “I” or “you”. This rule definitely gave me a mask that allowed me freedom in writing very personal content. So if you look at a poem like “Three Brothers” which is an absolute cornerstone to the book and extremely close—I was writing about my brothers and my relationship to them as honestly as I could but imagery and metaphor and form and voice somehow put up a boundary between the words and the person: “The ‘I’ here is not necessarily Barbara Nickel.”
I’m looking at your comment “…how you decide to write about people close to you”—somehow when I was writing those poems in Domain (“Three Brothers” is the obvious example) it wasn’t about choice; I had to write those poems. I did not check with my brothers first. I was open with two of them while in-process—in fact asked questions and in this process found imagery and narrative pieces—but there was never a question of permission. Perhaps this is because of the closeness of my family—there’s an underlying deep trust there—they knew that what I wrote wouldn’t be damaging.
Somewhat hurtful to me was the lack of response from my siblings to Domain. I dedicated the book to them, and I heard little or nothing in response. Casting poetical masks aside—for me it was about our house and our childhood and our relationships, very momentous and life-changing. But looking back now, I see (and obviously but it took years) that this was momentous only through my particular poet’s lens. If you look at ‘Flight’ (from “Three Brothers”) – the aabb tetrameter form that I chose, sustained over 20 stanzas, was excruciating to write, took a Canada Council Grant and years of my life, but that’s difficult—maybe not even possible—for my brother, the subject, to comprehend.
Perhaps these stanzas from the poem sum it up well:
…On the spring day
he climbs out of St. John’s and reaches
cruising speed, I approach
a footpath in that city. He flies
to Gander and returns: one flash
or all of my steps by the river,
weight of bags, dog shit jumped over,
stone by stone the high tower revealed
at the rate of my slog up the hill.
I’m approaching all of this in terms of poetry. I think if I wrote a memoir, the stakes and the terms would be entirely different.