Im arranging flights for family as it is a complicated sort of TP run, then Im doing it for them. It is CPH-LHR-LAX-HNL-SEA-LAS-LGW-CPH

Im trying to do it online through multi-city but it wont quote the HNL-SEA-LAS legs in Alaskan Air.

Before i phone BA to book them, can anyone help with that issue, ie am i doing something simple wrong?

And also, if i phone to book these flights through my account but using his credit card, will i be able to get free seat choice for them as im Gold and they are not. Or will BA not allow me to do that (which is what i suspect)