Rules: You are naming twins using the 2019 SSA name statistics! For a possible boy/girl pair, you must pick names that are equally ranked in popularity. You can pick the #1 names, Liam and Olivia, or you can pick #493, Derrick and April, and so on.
G/G and B/B Rules: For possible boy/boy and girl/girl pairings, you must pick names that are sequentially ranked in popularity (1-2, 2-3, 503-504, etc.).
SSA Top 1000: https://www.ssa.gov/OACT/babynames/index.html