As far as I know there is no way currently to sync persons in different trees. I believe there is a proposal in GEDCOM 7.0 to implement a _UUID for this purpose, but that is likely years away.
I have been on blogs where it has been discussed from a software perspective, and it is very complex.
So, right now it a manual operation.
I use a PC based program call GRAMPS. That is my master copy and I copy the data from Ancestry to GRAMPS, set a flag in Ancestry when done, then upload a copy to WT, and set a flag in GRAMPS when this is done. In effect, in sync as best it can be.