Hi Stelios,
Thank you for contacting Syncfusion Support.
Currently we were unable to set different height and width for each Carousel Item
We can customize the SfCarouselItem by using DataTemplate or else assign custom view to SfCarouselItem's ItemContent API. So could you please provide how you try to customize the SfCarouselItem, this will help us to provide appropriate solution.
Regards,
Rajkumar G