you cant split a data or log file to multiple files.

data and log files are always seperate, you cant have an data file which is your log file, unless for some reason you have named your LDF a MDF NDF instead but as the log file doesnt have a filegroup SQL knows its a log file.

you can add a filegroup and then add multiple files to the file group.

logs dont have a file group and having a second log is useless, but you can get that from sys.master_files, using the data_space_id which referes to the filegroup in the database

0 = Log files

1 = Primary

>1 = User defined filegroup

If you have more than one file in the data_space_id you have move than 1 file in the filegroup