Another reaction could be that Marinette pretends to cooperate with Adrien at first. By doing this, she can buy time and look for an opportunity to escape or get help. She might act as if she is okay with what is happening while secretly planning her next move, like leaving a clue for someone to find her or finding a way to disable Adrien temporarily.
Marinette can react by standing up for herself. She might confront Chloe directly and tell her that her actions are wrong. This shows Marinette's strong character.
Marinette could react with disbelief and assume it's some sort of joke at first. But when she realizes Adrien is serious, she might start to get really nervous. She could start fidgeting with her hands or her hair. If she's in the middle of doing something, like working on a design, she might drop her tools in surprise. Once the shock wears off, she would most likely be very happy and accept his invitation, but it would be a very flustered and excited acceptance.
Marinette might be initially shocked when Adrien steps in to protect her. She could be very grateful and show it with a shy smile or a simple 'Thank you.'
Alya would probably be super excited and start planning everything from baby showers to future playdates. She'd be there for Marinette every step of the way, giving advice and support. Nino might be a bit more reserved at first but would soon warm up to the idea and be a great source of comfort for Adrien, like helping him pick out baby clothes or build nursery furniture.
Eventually, the class might come to understand Marinette's decision. As they struggle to do things on their own, they realize how much effort Marinette had been putting in. This could lead to them changing their ways and maybe even trying to make it up to Marinette if she decides to start helping again.
Diane would probably be overjoyed. She's always been close to Meliodas and Elizabeth, and she would likely offer to protect them and help out in any way she can. Maybe she'd use her giant strength to build a special place for them to stay during the pregnancy.
She might be shocked at first. After all, she has no idea that Chat Noir has a kwami. But then she would probably be curious and start asking Plagg all kinds of questions.