Hi Smokin - congrats on your new babies! So it's possible that the eggs you saw out in the open were accidentally ejected from the area where the male pleco intended to guard them. If he has a cave that's open on both ends, the water flow could have pushed them out into the open. It's also possible if he's a first-time dad, that he pushed the eggs out of his preferred hiding spot just from inexperience. Or he sensed something was wrong with them, etc. But otherwise, we would normally expect the egg clutch to be closely guarded in a "cave", and for the dad to keep the babies hidden in the cave until they're ready to be free-swimming.
Yes, it is possible that your other fish/shrimp will prey on the eggs/fry. You can set up a separate tank, and I highly suggest using a sponge filter or at least a sponge pre-filter over the intake if you use any type of HOB or power filter, etc. And you do have to worry about cycling the tank. So if you're worried about doing something quickly, rather than setting up a second tank, you might be able to obtain one of those isolation nets that hangs on the rim of the tank. Or "breeder box", etc. Something that doesn't have openings large enough for them to get out or other fish to get in; but that shares the tank water and circulation in your main tank. For some amount of days they will survive on their egg sacks. But then they will have to convert over to plant/vegetable based diet (algae, zucchini, spirulina wafers, etc.)
Do you keep plants in the tank with them? You could take some free-floating plants and put in the isolation net/box or separate aquarium with them. Even if there's no algae present, there will be other "invisible" yummies on the leaf surfaces for them to feed on as they convert to prepared foods.
If it doesn't make it, it's not because of anything you did or didn't do.
