It is your trip, and organise it how you'd like. I'd do things a little differently to save time, stress, and money.
Your plan as you currently have it has a lot of zig zagging across the country and a fair bit of duplication.
This is your first trip to Europe and there is often a tendency in first timers to wish to "do it all" and, to a degree, I see signs of that here. It is always a good idea to tell yourself that you will return.
Geneva... Then, we'd like to rent a car and move to Lausanne
The best way to go between those two cities some say is by boat, others say by train. I agree that both are excellent. Lausanne is not a place I would like to try to find parking. It is a city which is as vertical as it is horizontal - the lakeshore is linked to the town and the upper town by funicular. Easy by train and funicular - less so by car.
While staying for 2 nights in Lauterbrunnen, we'd like to visit Jungfraujoch (depending on the weather).
Others here and I think you now recognise that that is nowhere near long enough in the Berner Oberland. The weather can vary so much, you really need to be on the spot so when all is clear you can shoot up to the top and enjoy all the walks. I find that the walks from Muerren and from above Wengen are excellent in many weathers but the Schilthorn and Jungfraujoch can be socked in.
I prefer Muerren myself. To be able to look out and feel that you can practically touch the mountains across the valley is incomparable, and because it is higher than Wengen you can look down across the valley to Wengen, and you can easily take the funicular up to Allmendhubel. I remember hearing an Alphorn recital there and eating raclette sitting on the terrace surrounded by mountains, then walking down. That was so nice. For me, 4 or 5 nights is a short visit there.
If we have time, we'd also like to see Bern and Murren.
Bern is the national capital, and is pretty nice, and has old fountains in the streets, but on a first visit the mountains are more unique. I spent a day there the first trip I took to the Berner Oberland - I made the mistake of staying in Interlaken but I did have the lovely pleasure of meeting and visiting with Fritz Hutmacher - sadly no longer with us - but in retrospect I would have done what I did the next year and actually stay up in the mountains.
You say Murren.. Do you mean the one I described earlier, or is that a misspelling of Murten? If Murten I would leave it for a third or fourth visit.
After that, we'd like to visit Lucerne and stay there for one night.
That barely enough time to do more than walk across the covered bridge. I would take the time for a ride on a ship on the Lake of Lucerne to the mountain called Rigi, or up in the revolving gondola
at Titlis. There is so much to do there. A car is of little help, and parking is expensive, just like it is in the Berner Oberland. Count on over CHF 25 a day. And if you drive you will miss the very scenic narrow gauge rack train between Interlaken and Luzern over the Brunig Pass. The car also can go over the pass but it is nowhere as scenic.
Then, we move to Sion area
It is very nice, but why backtrack? You already are in the midst of beautiful villages and fab towns. Great scenery.
You can get the Venice train from Spiez, just down the lake from Interlaken. It is the very same train which goes through Brig. Or a very similar one from Luzern which goes through more beautiful scenery as it flies through the mountains - at one point passing the same white church in a valley three times as it dog bones up through tunnels and spirals to gain altitude.
I hope you have have a great holiday. I'm with you in spirit. I'll be there in July.