The Short Spec Ops Combat Master Fixed Blade Knife Sheath will fit blades up to 6" long and 1 3/4" wide. The Long fits blades up to 8" long and 1 3/4" wide.
Yes. The correct Spec Ops Combat Master Fixed Blade Knife Sheaths for your knife is the "Short" sizes, which fit blades up to 6" in length and 1 3/4" wide.
The blade thickness of your Gemini Ultra Light exceeds the mas blade thickness that this sheath can accommodate.
Yes. Any of the "Long" Spec Ops Combat Master Fixed Blade Knife Sheaths will fit your knife.
Yes. The "Short" Spec Ops Combat Master Fixed Blade Knife Sheaths will be able to accommodate your Brothers of Bushcraft knife.
No it will not. The Prodigy has an overall length of 9 inches and this sheath only goes up to 8 inches.
Yes. You would want to choose the "Long" option.
Yes, if you have the 5-3/4" or 6" version the short models should work but, if you have the 6-1/8" version you will need to use the long models.