IIRC, there was a drouge set up for three aircraft at one time.
I think it was the Brits with their VC-10 or Victor tankers.
The new British AirTanker has also three drogues. The “Voyager” is already used for transport while first refueling operations already took place: http://www.aviationweek.com/Article.aspx?id=/article-xml/awx_05_20_2013_p0-580613.xml