Problem in inventory management

-- url of the page with the problem -- : www.lusmira.esy.es
-- HikaShop version -- : HikaShop [1503052315]
-- Joomla version -- : 3.4.1
-- PHP version -- : 5.5.21

Good afternoon,
I'm in big trouble,
I have suppliers that besides having clothes sale on my website, also has clothing sale on other sites, and when a product is sold to another site I get a lot of problems.
1 I have to wait a supplier of email (sometimes not enough) to give indication that has not already stock. And then I will give downtown stock.
2. I get blocked orders and other canceled due to lack of stock article.
3 The customers stop buying from lack of credibility of the stock management.
How can I fix this?
Is there any option where each vendor can give automatic low stock or add more amounts?
thank you