Yes, I think hiding and being ‘invisible’ is somewhat more normal behavior for paros than swimming happily around, – BUT it is also so that a breeding pair will be dominant in a tank and if there are other paroes these will stay away as best they can, – they will be chased. Paroes can cope – even in such a small tank, but it is definitely not ideal, – and its also a ‘waste’ 🙂 of a potential extra breeding couple.
If the male has eggs, yes, he will stay hidden for long periods. But the female in this couple will chase other fish away, so your nr. 2 male and female is probably not allowed anywhere, and may have to stay somewhere in the back of the tank.
I would really suggest to you that you seperate these fish, now that it is obvious you have got a potential breeding couple. Also because if fry is developed, non parent fish will be a threath to these.
I know its difficult because you might not want to split everything apart, – but unless the male is actually having eggs in a nest, – in which case it is not good to do anything of course. But if not, if you can get the courting pair into another tank, they will quickly reestablish the courting behaviour. And the other couple may be able to come more forward.
I really do think 5 gallons is too small for two pairs of paroes.