Merge 2 VCFs from different variant callers
The merge utility from SURVIVOR seems to be what you are looking for. I did not try it yet, but it seems to be especially designed to handle SV.

The simplest thing to do would probably to first merge your patients files together for each tool and have one multi-patient file per variant caller. Then I would merge the multi-sample files of the different tools.

Here is a detailed blog post describing the different challenges associated with merging structural variants from different callers and explaining the steps they took to address it. All the code to reproduce the pipeline is available on a github repo.