Had to refresh my computer, leading to all my files being... Well, obliterated. That sadly includes the saved world. the map was spread throughout. I will resume progress in 1.9 and attempt to rebuild pretty much everything I had done.

Thanks!

Here is the command to summon the stacked mobs you wanted

/summon Zombie ~ ~1 ~ {Equipment:[{id:iron_sword,Count:1},{id:leather_boots,Count:1},{id:leather_leggings,Count:1},{id:leather_chestplate,Count:1},{id:skull,Damage:3,Count:1,tag:{SkullOwner:MHF_Villager}}],PersistenceRequired:1,Silent:1,Riding:{id:"Villager",Profession:0,Invulnerable:1,PersistenceRequired:1,NoAI:1,Silent:1,ActiveEffects:[{Id:14,Amplifier:0,Duration:199980,ShowParticles:0b}],Riding:{id:"Wolf",CollarColor:0,Sitting:0,Attributes:[{Name:generic.attackDamage,Base:0}],Invulnerable:1,PersistenceRequired:1,Silent:1,ActiveEffects:[{Id:14,Amplifier:0,Duration:199980}]}}}

The reason you can damage them is beacause you are in creative try to hit them while in survival, and the reason for the zombie being killed could be you have your game on peaceful try checking that if that is not it i am not sure, but the invulnerable thing is fixed.

I hope this was helpful and if you have more questions just send me a meassage.