A single user may directly speak to a bot.
Once a group is set up, you can invite bots to it. However, you can't invite them during the creation of that group.
You need at least 3 people to create a group.
Unless I'm mistaken, then, the only way to have "2 users + 1 bot" in a chat is to create a group with 3 people, then invite the bot, and then remove one of those people.
Is there any other way?