You could share groups. This will prepopulate the users to the rosters. You may want to verify that your subscription settings are correct. Also you are better with the setting accept local as gateway and S2S subscription requests do not work correctly with accept all. If all the settings are correct it may just be a case of users are offline so the subscription request cannot be processed.
Well, thanks for your answer and your last sentece is the situation that I have and I just wanted to know if it is possible to change this behaviour, because the server knows anyway that the user will be accepted (it’s a standalone server without s2s)