Mh weapon will shoot the elements of the mh and oh is different story. If you freeze the enemies and you have 3x frostbiting, you can then use fire elements and the fire attack will deal 4x more dmg due to hitting a frozen enemies with frostbiting. The bleed in itself is also triggered. The frozen case I don't think will be there though if fire dot is put there. Not sure it is efficient but it's worth a try.
You can also have ice and shock as a nice combo. Main has ice with frozen. Hirling can have shock. Frostbiting increases dmg in general if enemies are frozen and high voltage increases dmg in general if enemies are paralysed. If done right, a loophole can be done. Good with amplify too. The hirling shocks many enemies and paralyses alot of them then you use your frozen attack. It will deal 4x more dmg if you have 300% high voltage. Then if hirling or you strike again, that attack will be 4x stronger with 300% frostbiting and this loop keeps going. This helps make sure you have a higher dmg before frozen explosion. It loops and loops on a hard group until you deal enough dmg to do it. Amplify loops it even more. When this combo is established, you constantly deal x times dmg then a different version of x dmg and so on. The enemies will be very paralysed, slowed and frozen too. This is theory but if put into practice, it will work hopefully. I haven't tried this one personally.
Fire and ice is a meh really. It's better for fire and shock actually. Fire and shock meant to boost bleed dmg as much as possible to defeat enemies in under a few seconds with inferno. I have tried this combo and I had great success with it and without relying on hirlings. It does still work and pretty efficient with hirling though.
Poison and shock can work though. Hirling could be a shocking hirling with lots of high voltage. Main character be green garden. The hirling goes first and if he has 600% high voltage or more, thats good. Then you attack with poison and poison cloud. Since poison already does huge dmg, it will do 7x more dmg when it hits paralysed enemies with 600% high voltage. Epic dmg will be dealt too. Haven't tried this combo personally but theoretically, its really good.
These combinations are real good but they require such high dmg to be multiplied so ALOT of planning and crystals. The green garden and shock idea though is the easiest to try out. Obviously an aim on how high a dmg you will deal too.
Amplify is a great combo for all of these combos but if you don't have wizard, thats fine too. Relentless is good for anything super high dmg if you're rogue.