Aganju: That's an interesting question. In the real world (and in the DailyGammon world) you are allowed to move "illegally" so long as the final position is a legal one.

At DailyGammon you are allowed to move a piece on the board even if there's one on the bar, as long as the bar is clear by the end of the turn. In live play it's very common to move two pieces together having rolled a double, and sometimes the lazy approach to moving a piece beyond a stack is to shove it into the stack and move the displaced piece to the final destination.

A computer or website that doesn't allow the moving of two pieces at the same time only does so because that option hasn't been provided in the playing interface. GnuBg does provide this facility. If you click an empty point then two pieces will be placed there if those pieces were on points appropriate to the dice roll. Similarly, both GnuBg and DailyGammon provide a greedy bearoff which may take up to four pieces off the board with one click. In the case of GnuBg it's not even necessary to have got all the men home as long as the move is unambiguous (eg. a 6-6).

My original teacher actually introduced me to the triplet of games in Tavli but it was a long time ago and I have no idea whether this situation came up. Given that two pieces can be moved together, I'd say not. If I were implementing Fevga, I'd apply the rules to the final position as that is the only point at which the opponent is affected.