That's tough.
I would almost want you to drop both and pick up Rinne and Mason.
Mason and Rinne may not get you as many wins as the other two. But they SHOULD post similar peripheral stats, and will at least be the #1 starter for their teams so you can match up favorable opponents and what not.
The problem with the tandem is that, as you found out, you will never know who will start the games. I don't think Boudreau even knows in advance. I have both, and I like it. But I'm in a daily start league. So I can switch it around day by day. If I had to start one for a week. I would be losin my mind.
It's tough to drop both...but in this case MAYBE it would be the good option since Rinne and Mason are good goalies too.
Team 1:
G, A, SOG, PPP, SOG, Hit, Blk, W, SV%, GAA, SO
C - Matthews, Crosby, Point, Seguin
LW - Miller, Tkachuk, Gaudreau, Kaprizov, Schenn
RW - Terry, Necas, Reinhart, Boeser
D - Hedman, Pionk, Hanifin, McNabb
G - Hellebyuck, Ullmark
IR - Wilson, Petry
Team 2:
G, A, PP, SOG, Hit, Blk, W, GAA, SV%,
C - Kopitar, Hischier, Rantane
LW - Panarin, Guentzel, RNH
RW - Marner, Kucherov, R. Smith
D - Makar, Hamilton, Heisknen, Dillon
G - Vasilevskiy, Hellebyuck, Ullmark
IR - Wilson, Aho, Theodore