I know we have to beat Oldham first, but if we do, which one do we play?

Lets assume Donny beat Barrow, its odds on, they are at home and beat them 72 nil last week.

By beating 3rd placed Oldham we took their spot, so had the easier of the 2 qualifying games away to Newcastle while Donny from a 4th place finish had to face London. That advantage carries over to next week as well with a home tie vs Oldham.

My question is, after that if we beat Oldham, are we still seeded 3rd and hence play 2nd placed Newcastle away again. Or because Doncaster finished 1 place above us in 4th, does the 3rd seeding end meaning we have to play London away to qualify for the GF?