Combining 2 Speedlites is sometimes the only way to produce the kind of power needed to have any effect when shooting during the day.
Most Speedlites produce something in the neighborhood of 80 to 100Ws of power, so combining 2 of them can result in faster recycling and more power.
Before you can use 2 Speedlites, yes, you’ll have to buy more stuff.
Sorry. Sometimes you really do need the tools and there are no workarounds.
Since I am a softbox user, I had to get something specific like the Lumopro’s double flash bracket speedring.
The bracket allows me to attach my favorite Small Octodome and fire 2 Speedlites giving me faster recycling and more power when I shoot in daylight hours.
Both Speedlites were set to the same group, group B.
The 3rd which was fitted with a snoot/grid was set to group C.
I adjusted its distance to give me just a hint of backlight so that it was perhaps 1 stop more than the main light my small Octodome.
After mounting 2 Speedlites to my cheap Cowboy studio boom, I realized I had better be careful and balance the boom with a heavier weight especially if I were going to walk away from the boom/stand.
If you favor umbrella-style light modifier then , then you might want to look at the Phottix Multi Boom.
The name or description of that piece of hardware is kind of vague if you ask me.
Portraits of Lianna
So here are some of my pictures with this 3 Speedlite setup, 2 inside the softbox and a 3rd as a accent light behind Lianna.
Let me know what you think.
The specifics like focal length and exposure info is under each picture.