It could also be strained. There might be some jealousy or differences in opinion on how to handle the situation. For example, one of them might want to be more involved with the girl during the pregnancy while the other feels left out, which could cause some tension between them.
In the fanfiction, it could be that there was some sort of mission or adventure that brought the three together. During that time, the relationship developed and the girl got pregnant. Steve and Bucky might then use their skills and resources to protect the girl and prepare for the baby. They could have to deal with enemies who might want to harm the girl because of the baby or their relationship.
At first, it might be a bit rocky. Tony, being used to his own space, might feel smothered by Steve and Bucky's over - protectiveness. But as time goes on, he'll start to see their good intentions. Steve's moral compass will inspire Tony to be a better person, and Bucky's loyalty will make Tony feel secure. Eventually, they'll become like a real family, with Tony looking up to Steve as a father figure and seeing Bucky as a cool older brother.
Typically, Steve and Bucky lemon fanfiction often emphasizes their deep emotional connection. It might show their loyalty to each other in different situations. For example, in some fics, they support each other through post - war traumas.
I really like 'Bucky's Redemption'. In this fanfic, Bucky is on a journey to fully come to terms with his past actions while Steve is there to support him every step of the way. It shows their loyalty to each other in a very touching way. There are some intense emotional moments as Bucky struggles with his guilt and Steve tries to pull him out of the darkness.
One common theme is loyalty. Steve and Bucky have a deep loyalty to each other that is often explored. For example, in many fics, Bucky will go to great lengths to protect Steve and vice versa.
There's also 'Forging New Bonds'. This fanfic focuses on the post - conflict relationship between the three. It explores how they start to understand and accept each other better. The writing style is quite vivid, making it easy to picture the scenes in your head.
One common theme is friendship. The OC often becomes a part of the friendship between Bucky and Steve, either strengthening it or causing some temporary rifts that they have to overcome. Another theme is redemption. Bucky, with his complex past, may find a new path with the help of the OC and Steve.
One possible aspect to consider in this fanfiction is the complex relationships between the characters. Steve and Tony have had their own share of differences and tensions in the original storylines. Steve choosing Bucky over Tony could be a way to explore deeper emotional bonds. It might also be about loyalty, as Steve's loyalty to Bucky is a strong theme in the Marvel universe. Maybe the fanfiction delves into how this decision affects the Avengers as a whole, causing rifts and new alignments within the team.
Friendship is a very common theme. These three characters often form a strong bond in fanfiction, relying on each other for support, whether it's during battles or in dealing with personal issues. For example, in many stories, they help each other overcome their past traumas.