Once you have created your custom block you have the ability to share them with other accounts.
Firstly, navigate to the My Blocks tab and click the drop down menu to share the block.
Then, select Share the Block.
You have the option to share the block with all the users or with specific ones by simply typing in their usernames.
Note: the users that you can share to will depend on your admin level
After you select the users that you want to share the blocks click Add Share.