France Switzerland

How you split your time depends on the interests of your family members. The way I plan with my family is to get everyone involved (at least those old enough to read) in looking at guidebooks from the library and deciding what they want to see. You will have to make some compromises, of course. I've never been to Switzerland so I can't speak to that part of your trip, but I could easily spend all seven days in Paris, especially as the first day is blown out with jet lag when I travel from the U.S.

The Bernina route is a rail line from Chur in Switzerland, over the Alps to Tirano in Italy. Therefore it is best fitted into your itinerary as a method of getting from Switzerland to Italy.

"7 days to visit France and Switzerland?" - What do you mean "visit" France? You would need many weeks to see the whole of France. Or do you just mean a short visit to Paris, 3-4 days is the absolute minimum.
How many nights is this "7 days"? You arrival day doesn't count.

"We will eventually travel into Italy for a part 2" - where in Italy? If it is northern Italy, OK to get to from Switzerland by train, if southern Italy you would need to fly.

Assuming you had enough time, you could do something like:
1) Fly into Paris, 4 nights
2) Train to Luzern (4½ hours) 2-3 nights
3) Train to Italy, Luzern - Chur - Bernina Route. Stop overnight somewhere along the route.
4) Continue on Bernina Route to Tirano, and train to Milan. From Milan you can get a train to anywhere in Northern Italy.

Some timings:
Train Luzern - Chur 2h08
Chur - Tirano (Bernina Route) 4½ hours
Tirano - Milan 2½ hours
Total over 9 hours, too much train for 1 day, hence above advice to stop somewhere en route. Plus, you almost certainly will be travelling on to somewhere after Milan.

Thank you for the info.

I say “ visit France” bc I’m not sure if we should just do Paris for a few days or do Paris + one other town/city before we head to France.

We plan to go to Venice for a few days then take a train down to Naples to meet up with my extended family. I’ve never been to Venice so want to stop there since we will be North.

I guess I just want to know an efficient route from France to Switzerland and what we should see if we only have 7-8 days.

"an efficient route from France to Switzerland" - that question can only be answered if you specify where in France to where in Switzerland. The two countries border each other, between two border towns you can just walk ☺
Assuming you mean from Paris to my suggestion of Luzern, the answer is by train, 4½ hours.

As your first stop in Italy is to be Venice:
Efficient route from Luzern to Venice - direct train via Milan: Luzern to Milan 4½ hours, Milan to Venice 2½ hours
Scenic route - via Bernina Pass, times to Milan as above, overnight stop recommended, then 2½ hours Milan to Venice.

If you only have 7-8 days, you hardly have enough time for Paris plus 1 stop in Switzerland. It will be rushed.

I believe you're going to run up quite high transportation expenses for this trip because of the jaunt through ultra-expensive Switzerland. And you're not going to have many days to enjoy that expenditure. Swiss rail fares are far from cheap. There is, however, a bargain way to take the Bernina Express. Take a look here: https://www.seat61.com/BerninaExpress.htm. You'll need to scroll down quite a bit.