You don't describe your setup enough for me to truly understand it, but ...
In Windows, only 1 application can read a COM port at a time, so to feed your COM stream to multiple applications, you need some sort of SW splitter to feed the COM signal to multiple (synthetic) COM
ports, & then each individual port can feed a
single app. You seem to have this already?
Also, having done MANY installations, one of my biggest headaches is poor quality Serial/USB adaptors. The problem is that
Serial (RS232) uses a +/-9v signaling scheme, while NMEA0183 uses 0-5v signaling. So your Serial/USB has to be capable of switching on that 0-5v signal, & many of the cheaper ones don't, or don't do it reliably.
FWIW, I've used a KeySpan 4-port Serial/USB adaptor for 16 years, since I first installed an
AIS, & it hasn't missed a beat. It's about twice as expensive as the
cheap ones, but worth it IMO.