These words are all ended with two "s" (should it be two "s's"??). How to pronounce the last syllable? Should we pronounced these words with two consecutive "s-s" sounds at the end or just one "s" sound is suffice?
They end in sCs (C stands for consonant). The consonants /k, p, t/ are voiceless, so /s/ is pronounced [s], voiceless. Pronounce Cs together, like this,
These words are all ended with two "s" (should it be two "s's"??). How to pronounce the last syllable? Should we pronounced these words with two consecutive "s-s" sounds at the end or just one "s" sound is suffice?
Is there a general rule for this type of words?
A footnote to Casi's answer. There isn't a 'last syllable' (unless by that you mean 'the first syllable'); they are all monosyllables. If you try to pronounce the final s as a separate syllable, your pronunciation will be wrong.
Words ended with "s" 
The consonants /k, p, t/ are voiceless, so /s/ is pronounced [s], voiceless. Pronounce Cs together, like this,
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