Sam would probably be very protective. He has always been there for Dean, and now with a new addition to the family in the form of a baby, he would see it as his responsibility to keep the baby safe. He might also be a bit of a mentor, teaching the baby about the world of hunting and how to handle different supernatural creatures.
At first, Sam might be a bit worried. He knows the dangerous world they live in and how having a baby in such a situation could be risky. But as time goes on, he would warm up to the baby completely. He would play with the baby, tell it stories of his and Dean's adventures, and be an important part of the baby's life. He would also be on the lookout for any threats that might come towards the baby due to its unique parentage.
The friends could play important roles in the baby's life. They could be like extended family. For example, their friends could introduce the baby to different hobbies and interests as the baby grows up. Carly could expose the baby to the world of web shows, Gibby to his unique form of physical comedy, and Spencer to the arts. Their friends would be there to shape the baby's world in a positive way.
There's also 'Dean, Castiel and Baby: A New Bond'. This fanfiction focuses on how Castiel, in his new 'baby' form, starts to understand human emotions better through his interactions with Dean. It has a unique take on their relationship and is quite engaging.
They could start off seeing the baby as just another supernatural problem to deal with. However, as the baby shows signs of innocence and dependence on them, they gradually become more attached. Sam might start reading bedtime stories to the baby, and Dean would teach it basic self - defense skills as it grows older. Their relationship would be a mix of love, protectiveness, and the responsibility of guiding this powerful being.
Castiel first wakes Dean gently from the nightmare. Then he sits with Dean and tells him stories about the great heroes in Heaven. He tells Dean that he is also a hero, and that no nightmare can ever truly harm him because Castiel will always be there to protect him. He strokes Dean's hair softly as he talks, which calms Dean down.
One key element is the relationship dynamic. Dean is often portrayed as the protector of baby Castiel. For example, in many stories, Dean will go to great lengths to keep Castiel safe from harm.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of 'dean and baby sam fanfiction' stories. Just use the search bar and type in relevant keywords like 'dean and baby sam' and you'll get a bunch of results.
Some fans would be extremely shocked and heartbroken. Dean and Castiel have a very complex and beloved relationship in the fandom, so seeing Castiel kill Dean would go against what many fans hope for in their relationship. They might be very vocal about their disappointment.
Dean would probably be very protective. He's always been the big brother looking out for Sam, and with Sam as a kid, that instinct would be even stronger. He'd be constantly worried about Sam getting hurt and would keep him close at all times.
Rick would probably be very protective. He would see the baby as a symbol of hope in their post - apocalyptic world. He might offer extra protection around their living area and ensure they have enough supplies for the baby.
Their friends would probably be really surprised at first. Orihime might be super excited and start making all kinds of baby clothes and accessories for them. Chad would be happy for them in his quiet way, and Ishida might be a bit more reserved in his reaction but still offer his support.