The Brotherhood of Mutants could also be antagonists. They might view the pregnancy as a sign of the X - Men becoming too domesticated and vulnerable. They could launch attacks on the X - Mansion in an attempt to disrupt Rogue and Logan's new - found family situation.
Some dedicated X - Men fanfiction forums might also be a good source. There are often users sharing and discussing their own works or ones they've found. However, these forums may require you to register before you can access all the content.
The Leaf Village authorities could be the main antagonists. Since Naruto is now considered a rogue, they would be the ones trying to hunt him down. They might see him as a threat to the village's stability and security.
Another possibility is that the main antagonists could be the leaders of the other ninja villages. They might view Naruto's godlike and rogue status as a danger to the balance of power among the villages. So, they could form an alliance against Naruto, leading to a lot of political intrigue and conflict in the story.
One idea could be that Logan is initially shocked but then becomes extremely protective. He starts preparing a safe haven for Rogue and their unborn child, like fixing up an old cabin in the woods. He gathers supplies and makes sure no one can harm them.
One popular 'rogue logan pregnant fanfiction' might be 'The Unforeseen Bond'. It delves into how their relationship changes with the pregnancy. Another could be 'A New Beginning for Rogue and Logan' which focuses on the challenges they face together.
Another option could be Mr. Sinister. He might see potential in Rogue's powers and try to manipulate her. He could also see Nightcrawler as an obstacle in his plan to use Rogue. So he creates various schemes to drive a wedge between them and make Rogue come under his control.
Maybe there are some traditionalists in their world who don't approve of their relationship or the pregnancy. These people could be the antagonists, constantly trying to break them apart or cause problems for them.
One potential antagonist could be a group of rogue ninjas who see Sarada's pregnancy as a sign of weakness in the village. They might try to target her to cause chaos. Another could be a jealous rival who doesn't like the attention Sarada is getting due to her pregnancy and her connection to Naruto.
Frieza or his remnants could be antagonists. They might see the unborn child as a potential threat in the future, especially if it has strong Saiyan powers. So they could plan to attack Bulma to prevent the birth.
The Vicious 6 could be the antagonists. They might see Gru's preoccupation with Lucy's pregnancy as a weakness and try to take advantage of it. They could plan to kidnap Lucy to get to Gru and force him to give up his new - found family life and return to his old villainous ways.