Personally I would discard them all. Some people might remove the spoiled top layer and then continue fermentation if they find the cucumbers below are firm and smell good, but that's up to you.

I think my main concern is what set of instructions you're following because weighting the cucumbers is so elemental it's possible there are other problems as well, like too weak a brine, too warm a temperature, any number of other issues that can affect product quality and safety.

To answer your other question, you want to keep air out, and one of the best ways to do that is to fill a food-safe plastic bag with additional brine and place it on top. A bag is flexible and with the brine is heavy enough to fill all the spaces and hold the cucumbers down. Also, if the bag should happen to leak, all you're adding is additional brine, so you're not diluting the solution.

I use a right-sized plate and put the brine bag on top of that but a bag alone should be sufficient. All Ziploc bags, even the garment storage bags are food-safe, so every possible size is available.

I've known of people to use all kinds of things, even a plate weighted with a sterilized rock. (And yes, that's OK.)

There are numerous fermentation threads on this forum with all kinds of advice and links to reliable online sources, so when you have a little time you might want to peruse some of them.

Carol

Thank you. It is a family recipe, but the family that cans lives 1500 miles away so I am learning on my own. You are right in that my error was elemental and that's the reason why it wasn't on the recipe. As everyone else that my grandmother gives this recipe to probably knows better, and she just didn't mention it to me. Thanks again for your help.
Ashley

Soft and slimy means spoiled. You need to throw it all out.