Sharing a custom field Extension Package

Hello,

I have an extension package installed in the customer database. In that extension there changes to the standard table (added some fields). Extension works fine and all good. But now I want to create another extension where I have a custom page which is accessing the same table and also accessing same custom field on the standard table. what base objects I use? Do I need to have that table as well? Will it be completely new one or should include that field? I have tried both and it wouldnt work. There must be possibility of sharing the fields are part of the extension , should they not? thanks.