(I made this! Some of it is from the original SFW Alphabet, but the rest is altered for a poly relationship! Feel free to use it with credit. If you ask, I'll send you a copy to make it easier!)
A - Affection (How both of them show it, who shows more, etc.)
B - Bonding (Favourite dates and time spent together)
C - Cuddles (Who likes to cuddle more, what cuddling both is like, how they differ, etc.)
D - Dynamics (The intricacies of the relationship)
E - Ease (How the relationship started)
F - Fall (Who fell for who first)
G - Game (Who gets the others to play and enjoy life more?)
H - Hugs (Who's the clingier hugger, how long hugs are in the relationship, how they feel)
I - I Love You (Who says it first, how long it takes)
J - Joke (Who is the mediator when things get a little tense?)
K - Kisses (What their kisses are like, where they like to be kissed, etc.)
L - Lean (Who needs the most assurance, how they support one another)
M - Mornings
N - Nights
O - Open (How/When they start opening up)
P - Package (How everyone complements the relationship)
Q - Quiz (How much they remember about their S.O.s)
R - Remember (Each one's favourite memory of one another)
S - Secure (How protective each one is)
T - Try (Who puts effort into gifts? Who's more likely to make gifts? Buy gifts?)
U - Unlikely (Who in their fandom would be the least-likely addition to the group?)
V - Vanity (Who makes everyone else dress a certain way for the aesthetic?)
W - Wake Up (List them in order of waking up in the morning + optional anecdote)
X - Xtra (Additional headcanon)
Y - Yawn (List in order of falling asleep + optional anecdote)
Z - Zone (What home life is like)