Grats on your naxx progression! grob is one of the harder fights in naxx because to run someone out, then back in as you have to run someone back out really slows the DPS down.
I've taken my 5boxing group and done everything but KT. KT is totally possible but a bunk 2nd healer wiped us a few times and discouraged the rest of the people helping.
I 5boxed my mixed group (Prot paladin, Disc priest, arcane mage, elemental shaman, moonkin) and had the help of a druid tank and a holy pali to seven man every boss up to gluth.
For Gluth I went in next day with my 5 plus a resto shaman, 2nd moonkin, holy pali, and another prot pali. so 9 people total including my 5. We did Gluth, thaddius, and Sapphiron.
Thaddius you can just cast slow fall on everyone or levitate if you have it. Spread your guys out so they won't hit each other with opposing debuffs. The enrage timer was a joke even without the buff, but that was becasue my group does really good dps, all of them above 3k, mage and shaman sometimes above 4k.
Just remember that the tank switch on stalagg and the other guy before Thaddius may mean you need to change your targetting to explicit for that fight.
i usually assist my prot pali and attack that target but i had to change it to /tar thaddius /tar stalagg which worked fine.
For sapphiron i had the resist sets crafted to ease healing on my guys. Getting behind an ice block wasn't difficult if you group up your guys, there is plenty of time. avoiding the blizzard is tough and really slows down DPS.
KT was not bad at all, it wasn't me "the 5boxer" that caused those wipes. just spread out for phase 2 and know that you will need to either switch windows quickly or be able to individually strafe a guy out of the void zone. Other than that it is essentially a tank and spank.
I also did vault of archavon and OS with my 5 and the feral druid/holy pali, was very easy.