We did it with one tank , 3 healers , 6 dps and impale was casted only once too per corruption. The only problem with one tanking are stacks from big adds in p2 but if u use healer cds and tank cds (prot pala) smart and rotate them u can do it easily. We went Ysera > Nozdormu > Alexstrasza > Kalecgos.