Some good advice here. I learn a lot of tunes from sheet music, but it is very important to listen to how the tunes are actually played. Listen for how the tune is phrased, how do the musicians give the tunes “lift”? Where is the stress, and just as important how is the offbeat dealt with? Tunes may be written with notes of equal length but it is rarely how they are played. How does the length of the note vary in different parts of the bar? Also important are the silences. The space between notes is just as important as the notes themselves. These are all things to listen for.
When you go to your session, treat the tunes where you “have to sit out” as an opportunity not a problem. A chance to listen. Don’t just concentrate on the flutes, listen to how the fiddles, the box players play the tunes as well. I find it very instructive to listen to how players of different instruments approach the same tune.
If there are festivals near where you live look for workshops. That is a chance to learn directly from experienced musicians.
Geoff