i send a group message but when someone answers my message it is in a separate message

Hello Bahamalover,

We see you have a question regarding group texts, and we'd be happy to help.

This page here helps to cover that particular situation: Send a group text message on your iPhone, iPad, or iPod touch

Based on what you're experiencing, it sounds like you may need to enable MMS. Otherwise, as the page notes, "All responses in a group SMS are sent as individual text messages and the recipients can’t see the other responses from the group."

You can check for MMS being enabled in Settings > Messages > MMS Messaging. Also check to ensure you have Group Messaging enabled here.

Cheers.