Ive broke down the steps ive used to create a combined animation below in blender
1>open blender and import your first animation
2>open a second window showing dopesheet
3>change dopesheet to action editor
4>in the action editor name the first animation something better than mixamo does
5>import your next animation
6>rename the animation to something useful
7>now you can delete the object for the second animation it wont delete the animation
8>repeat steps 5 to 7 until all animations are loaded
9>change the dope sheet to the nla editor
10>in the nla editor i click the down arrow so it shows like a button of the animation
11>with your first animation in the nla editor chose your pathline positions and add action script and select your second animation
12>repeat steps 10 to 11 for all of your animations
13>export your animation as FBX
