CCS synchronization

Question

Within CSS we talk about binary interactions. Does this prevent synchronizing multiple processes in one step? Example:

$P_1 ::= a.D$

$P_2 ::= \overline{a}.D$

$P_3 ::= a.D$

Let's consider the following LTS: $(P_1 | P_2 | P_3)\restriction_a$

Do I get $P_1, P_2, P_3$ $\tau$-synchronized simultaneously if an action $\tau$ happens or only two of them get synchronyzed and so I get $D|D|P_3$?