hi,
i just booked tickets for my winter break
1st ticket: oakland to memphis( 2 stops)
oakland to portland -alaska airlines(1st checked bag-25)
portland to houston-united airlines(1st checked bag-25)
houston to memphis-united airlines(1st checked bag-25)

my question is should i have to pay baggage fee for all flights if not, should i pay twice for alaska airline and united airlines separately ??

2nd Ticket: memphis to syracuse( 2 stops)
memphis to Charlotte-us airways (1st checked bag -25)
charlotte to boston -us airways(1st checked bag -25)
boston to syracuse-us airways(1st checked bag -25)

my question is should i have to pay baggage fee for all flights if not paying once at the starting airport is enough.One more question,do i need to check out and recheck in at every stop??

Are you flying all the way through with only a few hours at each layover or do you have a stopover en-route? If the former, then no--you pay the baggage fee once and it (and you) gets all the way to the final destination without any re-checking necessary. If you stop for ~12+ hours, you may have to collect and re-check your bags.

On the second ticket, you'll get all three of your boarding passes when you check in (either online or at the US Airways ticket counter). On the first ticket, when you check in with Alaska, they *might* be able to give you some boarding passes for United, but since AS and UA aren't usually partners, they may not be able to--in which case you'll want to visit the United customer service center in PDX (it's after security IIRC in the E concourse wing--don't leave security! You don't need to!) and either use one of the kiosks or talk to one of the people to get your boarding passes for your two onward flights. (It's also possible Alaska will give you boarding passes for your UA flights, but UA's gate scanners won't be able to read them, so it's probably worth getting UA-issued boarding passes in either case.)