Are you using robot command to execute? If yes, you can run with these arguments:
-d --outputdir dir Where to create output files. The default is the
directory where tests are run from and the given path
is considered relative to that unless it is absolute.
-o --output file XML output file. Given path, similarly as paths given
to --log, --report, --xunit, and --debugfile, is
relative to --outputdir unless given as an absolute
path. Other output files are created based on XML
output files after the test execution and XML outputs
can also be further processed with Rebot tool. Can be
disabled by giving a special value `NONE`.
Default: output.xml
-l --log file HTML log file. Can be disabled by giving a special
value `NONE`. Default: log.html
Examples: `--log mylog.html`, `-l NONE`
-r --report file HTML report file. Can be disabled with `NONE`
similarly as --log. Default: report.html
I suggest using -d argument. Indicate a different directory for each .robot file executing.
robot -d test1 test1.robot
BTW, why don't you execute them at the same time? You can see each log in one file.