So in other words your 2" vent that goes above the roof is going to need to be connected to the ejector pit, the lav trap arm, and the washer trap arm, at a minimum. The WC can be wet vented by the lav easily enough (not familiar with MA's plumbing code; a 2" lav drain and dry vent would definitely suffice, the IPC would allow 1-1/2").
The shower is trickier to wet vent: the UPC would require it to join the lav before the WC joins in (IPC doesn't care), and you definitely would need to join the washer in last, after the shower joins the lav. So it might be easier to send the drain towards the washer wall and pull off another dry vent for the shower. Then with the shower and washer both individually vented, the drains should combine so you only have one drain proceeding from that wall to the ejector. The vents in the wall could combine at a height at least 6" above the higher fixture's flood rim (so the top of the washer standpipe).
Cheers, Wayne
