I'm not sure how anyone is going to multibox 4h, Thaddius, Grobbulus -- seems impossible, and Grobbulus is only the 2nd boss in Abom wing. Gluth, Heigan (w/o cheat), Razuvius, Maexxna (cocoons), would be extremely difficult as well I think.

Patchwerk however would be extremely easy, as would Noth I think. Not sure about Anub'Arak, the kiting and OTing is going to be difficult. If you can get past Anub Faerlina will be cake.

Really of the 4 starting bosses (patchwerk, anub'arak, Noth, Razuvius) only 2 seem straightforward and easy for 1-2 multiboxers, and even then you would need a pretty beefy main tank, since you want him tanking all the adds that spawn (instead of an OT) plus boss, and he needs to grab the adds before they 1-2 shot any healers. i.e. you want a tank who has cleared Naxx25 multiple times (35k+ hp unbuffed) to multibox naxx10.