M.T.
It's up to you to train your daughter not to be so clingy and demanding of attention. She needs to know that your son is your child too and you love him just as much. Spend time with her before he comes home. Do not neglect his needs (whether it's your attention or your help with homework). Let your daughter know that when brother comes home, it is HIS time with you and if she misbehaves or tries to grab the attention, she will be gated in her room. Make sure to still acknowledge her before she demands your attention. You shouldn't only spend time with him when she's sleeping or with a babysitter. You need to do some behavior modification with her. With your son away at school during the day, she seems to feel that he is an unwelcome interloper when he gets home, and that she is entitled to ALL of your attention. You need to break her of this. Your son is right to feel resentful.