From the size (adult at 20"), brackish water requirements, and beedy eyes

, it sounds like a Dragon Goby. I have one of these and I totally know what you mean - I immediately fell in love with my little Melvin and went and bought a whole new set-up just for him.
You sound like you've done your research for your little rescues (bless you for taking them in). I add 2 teaspoons of Marine salt per gallon to make it 1.007
SG, so one rounded Tb per 5g should be about perfect.
Unfortunately, the poor things were probably housed in a tank with gravel bottoms. They feed by scooping substrate into their mouths and filtering it through their gills. They really really need sand, not gravel for their tank or they will end up with cut and swollen mouths

. I feed mine mainly frozen blood worms & tubifex worms and then he also scoops up crisps and flakes that make it to the bottom.
These little cuties are basically blind, so they can't be with aggressive fish who will pick on them.
They love a nice cave to hide in. Mine likes to burrow under the decor to make his own caves. It's really cute to watch him swish the sand out.
Mine adjusted after about a week or so, and now he's out and about at all times of the day and night. He doesn't even get scared when I have to put my arm in the tank. They're just the friendliest fish.
More than one per tank is kinda tricky though. Because they are nearly blind and so timid, one will likely out compete the other for food. Definitely keep an eye on them during feeding to make sure both gobies are eating.
I have pictures and videos of my little Melvin posted. You can get an idea of how they filter their food and how vibrant their colors become.
I'm so glad you rescued them. They are so misunderstood and mishandled; thanks for taking them time to read up and ask questions about them.
Oh, this site has some good info and pictures:
http://aqualandpetsplus.com/Oddball,...gon%20Goby.htm I've read a few other sites, but this one contains the most accurate information.
Edit: I didn't see right away that it was a link in aquarist48's post - there's more info there.

I'm a little passionate about these guys.
Edit 2: They also go by "Violet Goby" and "Dragon Goby"; searching those terms in the forum search will give you a few more threads, too.
