What I see a lot is a slide titled "Acknowledgments". Can either be position 2 or at end. I slightly prefer position 2, since you're not rushed, but at the end, can also make sense.
I would leave the title slide clean with the name of the presentation and the presenter (and perhaps an image or an explanatory subtitle). When you do an actual journal publication (even conference proceedings), it is obvious who the authors are and typically first author placement for main worker. A presentation is not a publication (it should have more explanatory material). And the others are not "co authors".
It is nice if you can mention a little of the contributions of the different people as you go through the acknowledgements slide: "Jane did the electrical measurements, Bob did the X-ray, Pete is my advisor, and NSF funded the project". (This is if you are main researcher). If you are the PI and a student did the main work and/or the slides, it is graceful to verbally let the audience know that.