Just quest the lowbies with the 70 out of group, just there to rez/heal if need be, and get to lvl 10. Then run up to shadowfang keep (its waaaaay better than deadmines btw its well worth the run, plus it puts you close to SM for when you are ready to move up)

Park the alts at the gate, you might have aggro problems to the first mob or 2, but after that, they are free to just stand there. Then take the priest and gather all the mobs up to the first miniboss, and holy nova the crap out of em, then have the wizard open the gate. Now the fun begins. Round up everything you can see in the main room, and aoe down. If you think you can survive, with renew and PW:S, round up more. Basically find out how many u can round up, then run em back to the gate and holy nova em down. You can skip looting if you want, it just takes time anyway. (I often bring along another lowbie solo who can loot everything, just so I get the copper/silver on my alts) I did it with a lvl 69 feral druid in crappy gear, and could pull most everything, and Ive also done it with an 80 prot pally, who at 30k hp laughs at the place.... Your priest should do fine. If you can handle it, run all the way to the first blocked boss, with the rest of the instance in tow, and aoe from there. You can then run out and reset, or go for the last boss, but in order for the lowbies to get exp/loot u have to pull the boss down the hall a ways...

You will hit 20 in no time, then you can either stay there for another lvl or 2 as it is quite easy, or run to SM Cath. You wont be able to pull as much with a 70 priest, but it should still be pretty easy. Just Stack Stam gear, keep PW:S up, renew yourself etc...