I am having some issues with multisites and have tryed to uninstall and reinstall the component but when I do my templates are still there and there seems to be more issues.

Could you please tell me how I can completely remove multisites so I can start a fresh with it please.

Thanks

First, JMS can be re-installed over it and the de-installation is not required to re-install it.

Before uninstall JMS, it is recommended to keep a backup of the "configuration.php" present in the master (just in case).
When you uninstall JMS, this uninstall all the patches.
The uninstall of the patches consists in restoring the files that were install at the moment that you installed the patches. This include the "configuration.php". As you may have change the DB login, password of this one, it is a good pratice to keep a backup.

If you are not sure that all the original joomla files are restored, you can always unzip the same joomla full package over the current master.
So that, all the patches will be removed.
Don't forget to remov

JMS does not save anything in the DB for its data.
So no cleanup is required in the DB.

Remark: Even when JMS is uninstalled, some slave site may continue working with multisite because the technology used by JMS is to modify the way that files are stored in the disk and how the MySQL tables are created in the DB.
This is the reason why we can say that in some circumstance, the overhead of JMS is 0 second because you can uninstall it and the slave are still working as multisite