As far as I know, BP processing runs on a single main thread, so there is no parallelism involved (that’s probably very fortunate, all things considered) so it’s one after the other.
If you need ticks to happen in an explicitly defined order, there is apparently something called tick groups and ways to ensure that one thing precedes another, but I have not looked into this, and I don’t know if it is exposed to BP or only available in C++.
I’m sure someone else has useful information regarding those things. Would be interesting to know!