I think .
If They get to enter what Hoseok looks like. He swore they will not like it ... Not at all ... They will end up hitting or hating ...

At Hospital: 

BTS suspect of him. They think what something happens to him hoseok after losing the Memory, they think what he would become another person.
They already knew from what they went to visit him yesterday they secretly saw him how he became arrogant and womanizing towards the other girls.
They were surprised and they were angry with him and it hurt them the way his almost brother hoseok changed, they want to protect Jamie but they have seen how she supported him and did not give up.
They realized that Jamie is able to do everything for him and fight for him. They can not bear to see her like this.
But they do not like how the new hoseok treats it.

Jin's POV:

Once I saw them scream and argue when she was lying on the floor, I got angry how hoseok treated you. From the door watching that, I could not stand it "it would have been me your boyfriend to protect you and I would not let you what I treated you in that way how he does it to you, Jamie".
* I watched from the door and wanted to help her *
She got up on her own and scolded him, I realized what she is capable of protecting herself and not letting herself be humiliated. That's why since I saw her at ASC, I knew what loved her and loved her form what it is. She is a surprising girl. More he loved her way of being and how interesting it was. But when I knew what Jamie  liked Hoseok,  inside of me I felt a pain knowing that the girl I like is going with another man, I decided to suppress my feelings and wish them the best.

 But my feelings towards her, makes me love her even more. The time passed, My feelings have not changed and I'm still in love with her. All the time I've wanted to treat her as my very special girlfriend for me.
She is special to me. I always saw her happy with hoseok, I loved to see her happy, that made me happy and made me feel jealous when I saw them together.

Knowing what I still have those feelings towards Jamie and I do not want to hurt her but could not stand to see her treated that way with the new hoseok, I want to take it off and make it mine.
I understand why Jamie chose Hoseok. But the hoseok you met is not here anymore, Jamie.
If he continues like this, who knows when his memories will return. I'll steal it in front of him.
I will show you how a real man takes care of his wife. If she gets hurt, I will not forgive you, Hoseok. .
I will never forgive him, Although we promised to be a family how you wanted but I can not promise that, hoseok.
I'm in love with her before you barely noticed, Hoseok.
I'm sorry but I want Jamie on my side, although I know that will not happen but I will fight my love for her, no matter what.
For what you know, We have a secret that we never wanted to tell you hoseok,   We are in love with her. 
We promised to be a family for Jamie for you but we can not promise that.
We love her how you loved her hoseok.
We are in love with her.

That is the secret that we have all had for her.

We never wanted to tell you because you guys  looked very happy even though we were jealous to see that.