British And Turkish Coins

well if they are gold they already valuable because of the metal itself but as for a premium on the coin you would want to know mintage, condition, etc..

As a general rule, yes, American gold coins do tend to have a higher collector value than non-American coins of similar age and mintage, because America systematically withdrew and destroyed it's gold coins in the 1930's. That "reduction in supply", combined with the "increase in demand" because of the larger number of coin collectors in America, results in a higher price.

Your "British" gold coins are most likely to be sovereigns. These were minted at half a dozen mints throughout the British Empire, and some date-mintmark combinations can be scarce, but the commoner types aren't going to be worth too much above their bullion value.

It's hard to say what the "Turkish" pieces might be without seeing a pic. Both the Ottoman Empire and the Republic of Turkey issued gold coins, and Egypt also issued Ottoman-style gold coins.