The victory places the Northumbrians fifth in North Premier on 46 points.
Alnwick found themselves 35-0 up with a hat-trick from Alex Robson plus a touchdown from Burn.
Eggleston then went over, converted by Moir for 42-0.
Kirby Lonsdale replied with a score of their own for 42-7, but right on half time Young went over for a 47-7 lead at the break.
In the second half Smith and Young touched down, one converted by Moir, for 59-7.
The visitors broke again and brought it back to 59-15, but a second try for Smith put Alnwick 66-14 in front.
Substitute Ellis then touched down, converted by Moir for 73-14 before Ellis was sin-binned for ten minutes in the closing stages.
On Saturday (January 29) Alnwick are away to tenth placed Rossendale.