I guess I have to report back, somehow my in-laws joined the trip and I had two reservations for 2 and 3 people. I did an online check-in exactly 24 hours before. First, for 2 people reservation, I got 11A,11B. For 3 people reservation, 11E, 11F, 12A.
Two aisle seats(11C,11D) became occupied in between two check-ins so I suspect Avelo begin assigning seats from 11A and in order.
I knew that person in 11D didn't buy a seat assignment, so I asked her and she switched the seat with me.