Four forgotten movies - crazy doctor, big hotel, western movie and Venice/Paris costume ball

I'm looking for several movies for my friend.

1) Probably 90's and TV Movie. The action takes place practically all the time in a large apartment building or something similar. A girl has gone missing there. Her sister (blonde) moves in incognito to solve the mystery of her disappearance. It turns out at the end that some crazy grotesque scientist who conducts sexual experiments on young girls lives there. I know how it sounds, but the guy had some kind of problems with his penis.There's also a cop, supposedly investigating, but he is near main heroine (a girl) more. The film had a stuffy, claustrophobic atmosphere, a bit like that of B-grade erotica. The atmosphere was also kind of futuristic, kitschy, I don't know what to call it, it just wasn't a typical 90's thriller (Sliver, Jade), rather a bit of a B-grade camp psychedelic.

2) Probably late 70s / 80s to 1990. The plot such a bit in the convention of Poirot or "Killed to Death." Several strangers are invited to some sort of party on the top floor of a massive hotel. A typical American apartment for the rich people (like from the TV series "Dynasty."). Naturally, the host does not show up, and as it turns out the apartment becomes a trap.
The heroes by means of deduction come to an explanation of the situation, what connects them to the mysterious host. I remember that they watched some video on VHS video cassette, which gave them some suspicions. One of the main characters was played, I think, by a mustachioed man typical of the for the 80's (Reynolds, Selleck type), probably.

3) A film somewhat in the genre of "Limitless Skies" (1952) or "The Last of the Mohicans" (1936). Perhaps 40's or 50's, something in style western movie from the colonial era. There were some group of soldiers in darker uniforms (so maybe French army) goes through the forest (where and for what ?, I have no idea). When they hoped that they had succeeded , they came out exhausted to some open area, and there was already waiting for them an enemy squad (sort of like the English) with rifles pointed at them (the sense was that they were walking in vain). There were also Indians Iroquois or similar to them.

4. Probably 50's or 60's. Again, one scene, but as someone who has recently watched should get it. A former carnival, costume ball (Paris or Venice) moves to the streets. One of the characters is running away through the streets somewhere. He is clearly being chased by someone. He tries to sneak between the merry cross-dressed crowd. Finally, in some dark alley, a murderer dressed as Harlequin catches up with him.