I am looking at a build that requires either of the following parts:
https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/2-644861-8/698419
https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/3-644486-2/698410
My question, is there a way to import schematics & 3D models or do you have to use the ones provided by EasyEDA via either jlcpcb or lcsc?
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
You have not specified which version of EasyEDA you are describing.
You have also not made it clear of you wish JLCPCB to assemble your boards using these parts or if you just want to design the PCB and assemble it yourself or have it assembled by some other 3rd party.
JLCPCB offer assembly using 3rd party components:
https://easyeda.com/forum/topic/PCB-Assembly-News-Global-parts-sourcing-Now-AVAILABLE-83a31e20f0474cd6a899cb13627e7094
You can import or if importing is not an option then you can build your own symbols, footprints and 3D models as described in the Tutorial.
You have also https://easyeda.com/forum/topic/Using-non-jlc-lcsc-parts-660302c192c74dd68971d58cd221b208
points you to Tutorials etc. that describe how to import things into EasyEDA and how to find, ecit or create your own ymbols, footprints and 3D models.