Thank you in for all the insight. Based on the trend of feedback, my current plan is to add a vent line for sink at the vertical drop into the main line, then connecting that vent into the ejector tank vent. The shower would still need to vent thru main line since both ends are vented. With that, I plan to move to 3" main line. The shower ptrap-to-vent does add up to be 64 inches from nearest vertical vent and code I see for 2" line is 60" max. But I think there is little risk of real world issues with vents at both ends of the main which I use am using as a wet vent at the 28" junction.
The idea to drop the vented lav line down into the shower ptrap was secure venting, but it creates a space available problem working within my concrete floor breakout space and with my drop location limited to within inner wall the line.