Welcome to the forum!
The name game is never ending and the opinions are split. Some terms that we use are are generic, some are more specific, some are ethnographically correct, some aren't.
Now with regards to the terms "shamshir" and "saif" I can only tell you my take on it as other forum colleagues may have different opinions. But that's the charm of if as it would be boring if we all agree on everything.
So, in my opinion, shamshirs are characterized mainly by their long, narrow and strongly curved blade of flattened triangular (wedge) cross-section. They can be distinguished further by their hilt into
"Persian shamshirs" (first photo),
"Ottoman shamshirs" (second photo),
"Indian shamshirs" (third photo) and
"Syrian/Arab shamshirs" (fourth photo).
For others, the hilt would be the defining element in naming the sword, so the saber in the second photo would be called "kilij," the one in the third photo would be called "tulwar," and the one in the last photo would be called "saif."
Is this ethnographically correct?!
Not really as in India pretty much all sabers would be called "tulwar," in Turkey pretty much all sabers would be called "kilij" and in the Arab world pretty much all sabers would be called "saif."
However, for me as a collector strictly ethnographic criteria are too vague and imprecise, so for clarity and conciseness I prefer to use more specific ethnographically inspired terms.