Transparent Image Layer Diffusion using Latent Transparency
https://arxiv.org/abs/2402.17113
https://github.com/lllyasviel/sd-forge-layerdiffuse
Or, if you need solid regions that overlap and mask out other regions, then generate objects over a chroma-keyable flat background.
Transparent Image Layer Diffusion using Latent Transparency
https://arxiv.org/abs/2402.17113
https://github.com/lllyasviel/sd-forge-layerdiffuse