Are you meaning nothing grows under the conifers? If so, well it won't - you need to plant a good 2 or 3 feet in front of them to try to get something to survive - even then, likely to need extra watering. Actual grasses require full sun, in the main - many disappear completely during winter, and that might be a factor to consider. Sedges such as Carex varieties (evergreen) are more tolerant of shade, but they do like dampish soil. Must it be grasses?

You need to go back to the drawing board & Google plants for dry shade, then decide what you want. Ornamental grasses won't grow but other nice stuff might...

I have carex planted under trees in dry shade and they have taken very well - actually rather too well: I have plants coming up everywhere and have now decided they're not worth the space. But of you really want a grassy look they'll do the job.
I'd recommend pachsandra terminalis and euphorbia. Vinca will also cope and give you some colour. And snowdrops.

I really really wouldn't have Carex pendula. I planted it against advice getting on for 10 years ago and am still getting seedlings even in containers years after getting rid of it. Crocosmia might grow there on the edges- looks a bit grassy and flowers too.There's a range of colours from yellow through orange to red. Just try a few and see if they do flower there.
You'd get the leaves anyway. Fern Polystica setiferum will grow in pretty dry shady places. And a tip - when planting anything in dry shade make the planting hole a bit bigger than you normally would and mix some gel crystals with the soil that goes back into the hole. Can make a big difference - I got some poor flagging perennial geraniums to take off and do well with this little trick..
I have an Arum metallicum under a conifer hedge. Not spreading but surviving - might respond to this trick.
You might try Epimedium rubrum too, using the gel trick. Spreads brilliantly when happy and had marvellous spring foliage.
Nothing here guaranteed but worth a try perhaps.