For the time crunch - perhaps you could take a picture of the progress so far - and present that to the bride and groom - rather than take short-cuts on the making process that you might regret. ???
As to the batting/wadding - I have a quilt that is over 20 years old that I used Mountain Mist polyester batting that was glazed - (no washing of that before using it!!!!!) - we use it as a couch quilt and it has been washed many times. The batting has not bunched - but it was quilted "all the way through" -