I would suggest OpenToonz, which is open source & free, and excellent for all sorts of animation. If you intend to import pixel art, the render options have an option to keep it pixel art when it is scaled up, if necessary (output settings-->Resample Balance-->Closest Pixel (Nearest Neighbor).
OpenToonz does tweens, frame by frame, has a very nice timeline, works with layers (called levels), does parallax layering using pseudo 3d space, and camera control is very simple. Multiple cameras can be set up for easy view switching. A wide range of effects via a node editor are available.
To export to various additional formats, the FFMPeg encoder must be installed and OpenToonz be told where it can find that (preferences).
Very professional animation software (it is used by Japanese animation studios for feature-length animation films), and it may take you a couple of days to get used to it. Very, very, powerful. It's amazing it got open sourced two years ago, and by now all the kinks and bugs have been ironed out. The GUI is quite pleasant. I love animating in OpenToonz.
But as far as I am aware, you would still have to invest in a video play extension like GMLvideo to play the result in GMS.
Get the latest builds of OpenToonz at
https://github.com/opentoonz/opentoonz_nightlies/releases
PS
@deem93 it's a shame Game Studio doesn't include a timeline editor with key frames, and the option to animate anything like some of the main competitors, because I would have advised you to use that instead. That said, the primitive timelines function in GMS might help with cutscenes as well.