Paris is a HUGE area.
Where or what hotel exactly, are they staying at?
There are many sections in Paris. Called "Arrondissements." There are about, 20, arrondissements in Paris. For example.
My Husband is from there. And no, French men are not all wonderful like in the movies.
We have been there.
Many things to see, of which it is touristy.
AND there are, MANY pickpockets there.
It is a nice place.
A person can have a nice time, simply by, walking around and seeing the sights that way. MANY small cafes/shops/restaurants are discovered that way. Many of which are not even listed in "tourist" books.
You do not HAVE to have a reservation, to eat at the many restaurants or cafes there. Many times, we just walked into one. And got a table.
Take a French dictionary with you. Unless they speak French.
Also know...that in Europe they are very multi-lingual. MANY of the French, do speak English. I went around France by myself and did fine. Anyone I encountered, DID speak English. Just be polite and respectful. It is a different culture.
Beware, that in Europe, people walk everywhere or take the trains/metro etc.
I hope, your Mother In Law, is mobile, able bodied, and healthy and can walk???? For long periods???
Paris also has bad smog. The air quality, depending on the weather, is pretty bad.
The city is not all handicap equipped. Sidewalks are not real wide. Many small and narrow streets made of uneven little stones. However, they have the best paved modern roads/highways and signage. Depends on the areas, that they go to.