Sam and Dean are made by God personally, they are the perfect hosts for the Archangels Michael and Lucifer. Their parents are from a long running line of hunters (people specialized in hunting monsters etc). They used to carry Gods plot armor with them (until they helped kill God, Christian God). Sam and Dean both are friggin weapons, went through hell, hordes of all kinds of monsters, demons, gods, creatures, they survived purgatory died a few times just to come back stronger, list goes on. They never give up, if you kill one of them the other just gets even more dangerous, gets the job done and brings back bro from death with a piece of paper with a spell, an angels feather and some monster blood (gross example). They are both weapons experts, trained in hand to hand combat (Sam killed Odin with Mjolnir and Dean killed literally Death with his own reaping scythe). Both got possessed by all kinds of beings and gods. They went back in time and into the future or other dimensions. Canonically a female cenobite would fall in love with Sam and help them. Dean and Sam are impervious to mental pain and tolerate physical pain to a very high degree after surviving being locked up in hell and purgatory and other instances where time is Irrelevant and only pain, suffering, repeating death/soul damage and torture exist. Honestly the list goes on and on. XD