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It should not cause a problem if you decide not to declaw the younger cat. The older cat will defend himself with his teeth if he has to but it won't be nearly as effective as if he had claws.
It can take up to a month or longer for them to accept one another. If your older cat has had some run ins with others, he might feel a little inferior but this is ok.
I think that they will be just fine together with time.
You do not have to declaw the younger one just because the older one has no claws.
Let me know if you have more specific questions about this.