Stored procedures

hi, we have integrated app environment where one is custom developed and other is product. we have sql server as common database but different db schema. its large app and all stored procedures written in bespoke app, we have directly connected to product db to get any data needed for bespoke app. means SP will have mix of all calls to both the db. now we decided to move to new product but the major issue us with SPs. what options we have here