How to make scheduled Feeds importers run consecutively?
You've entered that territory where you would be better served by a custom module than trying to force Rules to do what you want.

If I were posed with this problem I would do the following:


Create two CRON jobs one for each of the importers in a new module. See hook_cron().
Turn off all of Feeds default importing for those feeds.
Install Elysia Cron.
Schedule your cron jobs with Elysia to run at appropriate intervals leaving enough
time for the first to complete before running the second. 
For extra credit you could programatically check that the first import is
complete before allowing the second to run.