|If the present CRT monitors have....|
"- a MDA or HGA mono display - (black and white, or amber, or green)"
"- a CGA display - 4 colors including white, or mono, 3 shades of grey and white"
"- an EGA display - 16 colors including white, or mono, 15 shades of grey and white"
... then you cannot connect the physical 9 "pin" d-sub probably female video port directly to a monitor that has a 15 pin d-sub connector, and get a display, no matter how many pins it has on the physical 9 "pin" d-sub port, even if you use a 9 pin (probably male) d-sub to 15 pin (female) d-sub gender adapter.
As I said above...
"....if it's possible to change the display adapter's card, you need to change it to one that supports VGA video that has one or more 15 "pin" female port(s), that has the right type of contact arrangement on the bottom of the card - likely ISA, or a lot less likely, PCI "
If it's not possible to change the display adapter's card, as in, a physical card that can be removed, then you cannot connect an LCD monitor to the 9 "pin" d-sub port any way I know of. You can only use a CRT monitor that is a type that is compatible with the type of video adapter.
LCD monitors that are MDA, HGA, CGA, or EGA compatible have never existed as far as I know.
MDA, HGA, CGA, and EGA display adapters all have a digital output.
VGA display adapter ports all have an analog output.
Newer video adapters on a removable card that have a DVI port are all wired up to support the DVI-I standard - they support both DVI (digital) output and VGA (analog)output - if the card does not have a 15 "pin" d-sub female port, or if it does but you want to connect two VGA monitors, a standard DVI-I to VGA gender adapter plugged into the DVI port outputs VGA video. The digital output is not compatible with the MDA, HGA, CGA, or EGA monitors.