Is there a way to resize a group of objects like one large single object?

Current version (0.10.2) allow to resize each object in group, not the entire group.

This is not possible yet, but it is covered by the following pull request:

Hopefully it can be accepted for Tiled 0.12. Tiled 0.11 is currently in final stages and no longer accepting such large changes, and the change isn’t completely ready yet.

Thanks for your answer!

For future reference, the above pull request was merged and then improved upon. The feature was released with Tiled 0.12.