First sneeze :

 

“À vos souhaits”/”À tes souhaits” depending who you’re talking to, meaning “To your wishes”. 

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In French, you can use either “tes” or “vos” (which are both French for “your”) depending of the number of persons you’re talking to, but also of their position in relation to yours : if they’re especially older, if they’re your senior in any way or if you don’t know them very well, you’ll say “vos”.

 
If addressing a child, a person about your age, a friend or a family member, you’ll sat “tes”.

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Second sneeze :

 

“À vos amours”/”À tes amours” meaning “To your loves.”

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The answer of the sneezer :

 

“Merci, que les vôtres / les tiennes durent toujours.”

 

Meaning:

 

“Thank you, may yours last forever.”

 

As for ‘vos/tes’, decide whether vôtres or tiennes is more appropriate.