This was probably a behavior that started prior to neutering - part of why you are encouraged to neuter prior to 6 months of age.
It can take up to 2 months for the hormones to get out of their systems. Spraying them with a squirt bottle I do no encourage. No matter how good your aim is, they could move - you could get them in the eye or ear causing damage. I do not like the use of a can of air, either.
Have you been cleaning up the urine with an enzymatic cleaner?
Have you gone over the house with a blacklight looking for places they've sprayed?
Have you tried putting tin foil when they spray?
Has their urine been tested for a UTI?
Also - are they definitively spraying, or peeing? (Spraying would be backing up, tail erect, to pee - just peeing would be squatting)
Some links to read:Litterbox location secretsCombat Cat Urine
More things to think about.....you can try diapers to curb the habit. Some vets have had success with medicating cats to stop this behavior. When did the spraying start? Did anything in the house change that could have caused them to start (other than them being intact)...could be as simple as litterbox location, type of litter, change of food, or something you changed, like cleaner, air freshner, new couch, etc? Do they always go in certain places? Are there certain things that deter them from spraying?
I also agree declawing probably made things worse. What's done is done. And giving them up will not be easy - now that they are declawed they must be indoors cats & most shelters would euthanize them immediately for poor litterpan habits. I encourage you to stick with it, I know it's hard to live with, esp. expecting a child - but the alternative is a fairly likely death sentence. It can be overcome, I've worked with adopters before, but you have to just keep going.....
You have a wealth of advice & knowledge here with TCS - if you are willing to keep trying, we can keep bouncing ideas at you.