Hello,
If we can say: Peter's the best friend of mine
Can we say: Lewis's the best friend of mine
Or do we have to say: Lewis is the best......
Thank you for your help
(I'm not a teacher.)
In words which end with s, it goes like this:
Lewis'
Swiss'
Beasts'
Just an apostrophe, no extra s.
Also, the sentences you wrote should be like this:
"Peter is a best friend of mine."
"Lewis is a best friend of mine."
OR
"Peter is my best friend."
"Lewis is my best friend."
Do you understand why?
I would use the full form for a name ending in an "s."
The idea of a contraction is to save time in pronunciation. "Peter's" instead of "Peter is" saves a syllable.
"Lewis's" would basically be pronounced the same as "Lewis is." So there is no point to trying to make it a contraction.
In formal writing, I would use the contraction with neither.