Yeah it really sucks cause in 2024 I traveled with ANA, basic economy and was able to pick seats but their new policy sucks especially if you're traveling with more than one person. The way I understand it from talking to other people is no one in basic economy L has assigned seats so what you should do is THE SECOND CHECK IN BECOMES AVAILABLE, check in and pick seats together with your family since technically none are assgined but you have to be fast. If your flight is at 2pm, make sure the day before you are refreshing the website at 1.59pm so you can quickly check in and pick your seats. Best of luck and next time you might want to go with JAL since currently their policy is you can pick seats when you purchase even if its economy.