Hi! Can you please tell me if there are any changes to make? I'm going for a casual conversational style. Many thanks!

• ‎The brothers looked alike but had very different temperaments.
• Some people feel bad when they see him feeding his python live mice.
• The embarrassed boy admitted that he hadn't really put much effort into it.
• The girl was ashamed of herself and apologized for being rude to her mom.
• The sleeping little boy didn't hear the doorbell.
• The wide-awake young lady answered the landline at midnight.
• Some people say that a conscious citizen cares about the environment and tries not to consume too much.
• Since my sick son couldn't handle the chores, my healthy son took care of it.
• The sick man couldn't bear the pain any longer, and he ended his life.
• The guy who wasn't feeling well caller in sick to work.

Question

Hi! Can you please tell me if there are any changes to make? I'm going for a casual conversational style. Many thanks!

• ‎The brothers looked alike but had very different temperaments.
• Some people feel bad when they see him feeding his python live mice.
• The embarrassed boy admitted that he hadn't really put much effort into it.
• The girl was ashamed of herself and apologized for being rude to her mom.
• The sleeping little boy didn't hear the doorbell.
• The wide-awake young lady answered the landline at midnight.
• Some people say that a conscious citizen cares about the environment and tries not to consume too much.
• Since my sick son couldn't handle the chores, my healthy son took care of it.
• The sick man couldn't bear the pain any longer, and he ended his life.
• The guy who wasn't feeling well caller in sick to work.

Answer

You generally wouldn't say things like "the brothers" and "the boy" and "the girl" and "the lady" and "a citizen" etc in a casual conversational style. It's all quite formal. In casual language, native speakers are much more likely to say "he" and "they" when the context has already been established. If the context is not yet established, then you need to establish it first before using "the" else people won't know who you're talking about.

In the last sentence there's a typo - change "caller" to "called".