Opening new lines in Costco using T-Mobile offers

i have Go5G Next plan. Recently did port and port back in as win back customer. Still considered as old customer for bogo offer. We have 3 lines and planning to bring 2 more lines using bogo offer. Want to port in these 2 lines in Costco to take advantage of $400 promo. TM is also offering free 16e (other android phones like S25) for new ported lines. Do we need to do both the promos same time in Costco? Can we add lines in Costco with $400 promo and take advantage of free phone promo later in 14 days? That is what TM store rep told us (he things free 16e for new port in lines going to stay for some more time). is this possible to make use of all these promos ($400 costco, bogo and free 16e for each line)?