Is there any way to share the extensions between the master site and the slave sites without reinstalling the extensions on the slave sites?

Thanks!

If you want to share an extension, you need that it is define in Joomla.
So you need to install and create (link) the MySQL tables for this extension otherwise the extension will not be know by joomla like you have not installed it.

Thanks for your reply.

So how can we share extensions? If we reinstall an extension in the subsite, then the extension in the subsite and the extension in the master site will be different instances, right? Can I reuse the same instance of the extension of the master site?

I suggest that you have a look in the tutorial video 0.a (concept) www.jms2win.com/tutorial#jms12x-0a
and in tutorial video 16
www.jms2win.com/tutorial#jms12x-16

As explained the sharing of an extension consists in sharing of MySQL tables.
So if you install (not shared) an extension into a slave site, it will have its own MySQL table that you can see with the JMS tools (table tab).
If you decide to create a slave site that share the extension the you will see that MySQL table will be a link to another website (the one that physically contain the table).