Voitures mystérieuses sur d’anciennes photographies de famille

Dear friends of classic cars,
Thank you very much for your assessment of the vehicles pictured!
Very interesting.
I wish you all the best.
Thank you,
Rolf

I think not a 1924 5HP Citroën because high pressure tyres 700x80 on photo'car.
The car was presented in 1921 for the first time in Salon de Paris (prototype) and sold in 1922, 1923 and few months in 1924 with these tyres.
New ones 715x115 Confort will be presented in March 1924.

The second car is not a type 40 Bugatti, but a type 30. The small brake drums at the front and large ones at the rear are typical. The headlamps are unusual for such a car.

1924 C3 Citroen 5HP Torpédo

Well done, Ariejan! Yes, I also think it's a S.A.G., which was actually a licensed copy of the La Hispano-Suiza designed by Marc Birkigt and built in Barcelona.
The S.A.G.s produced in Geneva were marketed under this name for the Swiss market, while in France and Great Britain they were sold under the Piccard-Pictet brand, which was the name of the workshop where they were built.
The S.A.G. brand was discontinued in 1911 in favour of Piccard-Pictet.

The second car is a Bugatti Type 40.

The car on the lead photo with its Swiss number plate also is a Swiss make: an SAG (Société d’ Automobiles Genève) of about 1907 or 1908. Around that time it was renamed Piccard-Pictet (or better Pic-Pic). If this car was already called a Pic-Pic or still an SAG, I cannot tell from this picture.
The second photo is too vague for me to identify, and the last one too easy ... (Citroën of course, the exact model is for others to determine)