Never heard of the cocktail before. Interesting. I have been considering the Irish cup ritual since I'm afraid of a candle getting blown out by the wind or the sand likewise being scattered. There are several versions that vary from super religious to super informal - some just bride and groom with others including the whole family of bride/groom. Here are some links I'm referring to as I work out what we want to do:

http://www.celebrateintimateweddings.com/lovingcup.html (family ritual)

http://www.irishgaelictranslator.com/translation/topic33797.html (bride and groom ritual)

http://www.weddingplanningwords.com/wedding-ceremony-of-celtic-cups.html (bride and groom ritual + pebbles)

http://irishweddingcup.com/ (very religious)

There are lots more, but these should help you get started if you're interested

We are doing a Fisherman's knot. We can't do a candle because it could blow out, I'm not into the whole sand thing either. The knot is very hard to untie, the tighter you pull, the tighter it becomes. I plan to put it in a shadow box after the wedding to remind us.

Like the fisherman's knot idea.

One thought I had was a candle my 3 children and his 1 son light with us.
Would need 6 candles or a candle with 6 wicks.

Right now, this idea isn't very feasible... so I'll see if the Pastor has some ideas.
If he's been a Pastor for 35 years, I'm sure he's done 1 or 2 weddings before! (LOL!)

The 6 wick thing is doable and TOTALLY DIY friendly. Yah- save $$

Plain wax is cheap and you can melt on your stovetop and color with a regular crayola crayon. I don't think wicks are too pricey either. If the supplies are still too pricey, the DIY way (my grandma does this all the time) is to melt down your old candles whose wicks have burned all the way down on the stove. Make your wicks ahead of time too: http://www.ehow.com/how_5936_make-own-wicks.html.

The holder can be anything you usually see a candle in if you want to buy something empty, but when I was a kid we used to do them in the dirt or sand to get a shape without a container. You could probably get the container cheap on clearance at Michaels or Pier 1 or Goodwill if you wanted.

It might be cool to do the project with your kids to make it even that more special as you are all creating the "unity" candle together as well as lighting it together.

Just my thoughts for a way to do it on a budget