I have several Profoto soft boxes and use one of their Speedlite holders that will hold two Speedlites inside the various soft boxes which mount into the outer ring, that ring can be rotated to rotate the soft box too. If just holding Speedlites the holder can easily hold 4. The thing is built like a tank, but is almost $200 too. It will outlast me for sure.
You can also get 3 Speedlite holders that hold the Speedlites at 120 degrees to each other. The holder mounts on a typical light stand fitting too. They are $20-$30 depending on quality.
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