2 people on separate bookings with no seats selected so far - I assume I'd be randomly allocated if I don't pay, not sleect at check-in...?

Can I take the chance on the first check-in, then select the second seat to be next to it [assuming available - there's a fair bit of space at present]. And/or, can I change seat after check-in for a fee [i.e. in the event that person A gets stuck with no free adjacent seats].

​​​​​​​Cheers.