Hi,
yes this is possible, we have a Image field type and it works like Avatar field (avatar field is a image field type).

In my case, user registered as a team, so in user registration form the team need to upload 3 profile picture (members of the team), and if possible these 3 images (profile pics) will be shown in their frontend profile menu.

You can show all these images in the profile, but keep in mind that the avatar in only one, it is uses in the lists and integrations (like Author plugin). Of course there are multiple possibilities to show avatar as you want, for example with content plugin (so for example you can include it in a module or in a article) or template override (this is a Joomla feature and require PHP knowledges).

All I want is just to show these 3 images / profile pics (and their position in team) at team's frontend profile menu. It's not about creating article with its avatar, because the members not create any article.

Hi,
all images field type will be shown in profile like all other fields automatically. You can test how to create a field and how it will be show in profile with the free version (of course free version allow you to only create text field type but the concept is the same).