Hongjoong
He would be really surprised because he wouldn't be expecting you to come because of your job, you said you couldn't get time off, but when he say you he would scold you for lying but then hug you so tight you couldn't breathe.
Seonghwa
He would kinda suspect this kind of thing from you. He would still be surprised but he would've known you would show up at some point so he would just smile and probably do some ageyo.
Yunho
When he saw you in the crowd he couldn't stop smiling and waving at you. When the concert was over and he met you backstage he couldn't help but hug you and maybe kiss you all over your face. He'd be so happy.
Yeosang
He would do everything in his power not to acknowledge you. Why? Because whenever you were around he would not be able to stop smiling and if he smiled to much the fans might notice something was up.
San
When you surprised him at the hotel you were talking to him on the phone. When you walked into the room he stopped talking and stared at you. He was so happy he almost dropped his phone running to pick you up to give you a hug.
Mingi
Mingi would notice you in the crowd before you even notice him. He would be backstage and see you in the front row waiting for the concert to start. After, he would pull you into a hug and tell you how much he missed you.
Wooyoung
He wouldn't notice you in the crowd but he would notice how one of the makeup artists were wearing a mask. When he asked about it you revealed yourself and made him smile ear to ear.
Jongho
He wouldn't know how to handle himself. While the concert was happening he would blow kisses at you, wave, send hearts etc. He would make the crowd scream in happiness but confusion at the same time.