can i connect two (usb to serial eg. FTDI)?
Assuming you’d be using an FT232 or equivalent. The answer is no, you cannot directly connect them as they are USB device only and you’d need one of them to be a USB host.

I know of no serial to USB host chips.

What you could use is on one end is a microcontroller with USB host capabilities. This would, of course, require the appropriate programming to act as a bridge.