Umbrella/Speedlite Setup for Wedding Group shots in Church Sanctuary?

I have a few weddings coming up and am thinking of slightly changing up how I do the sanctuary portraits (mainly group/family shots). Currently I use two Canon Speedlites (580 ex ii), synced with Cybersyncs, on light stands with small white shoot-thru umbrellas. The coverage isn't always the greatest, and the light isn't very soft. I typically have the stands setup offset from the middle, on either side of the stage, pointing in - usually standing up in between church pews.

*Due to budget, I need to make the speedlite plan work for now. Would love to upgrade to some more powerful strobes down the road.

I'm wondering if nicer/larger umbrellas would be a better solution? I was looking at either a 45" or 60" Westcott or Photoflex, with black backing/silver or white lining (http://www.bhphotovideo.com/c/product/42512-REG/Photoflex_UM_RUT60_Convertible_Umbrella_60.html). Is that going to be too soft for what I'm trying to do? Does a larger umbrella typically provide more coverage.

As you can tell, I am not an expert when it comes to this type of lighting. Any help would be appreciated. If anyone has any examples of setups that could be referenced, that would be even better.

Thanks,

Jamie