At a casual glance it looks like your products are mostly [processor] connected to a network of CAN and/or 4-20mA devices. Not possible to back-port newer control modules to older product lines?
That said, impressive that you are handling all of it on your own. Hire somebody!
I have back-ported somethings, but really a large chunk of the products had terrible technical decisions before I started. I spent the first couple years just dragging the company back from the technical and financial brink. I'm slowly eliminating old products from our sales sheet in favor of ones I engineered. So it will eventually be ok.