Im stuck

You can't really do much if you only have red units, you need to make a balanced team with some other colors. Use some of your 4 or 3 star units, they don't need to be 5 stars to be good. Lunatic is supposed to be very hard and you are supposed to make teams that counter the units in those maps.

I had Robin (m), Marth, Lucina and Camilla (robin and Camilla 4*)
And they ate me alive. I had to use the blessings. What else was i going to use them on i had 10 blessings so i just used 4 of them for 9-2, 3, 4 & 5

Or, you know, you can wait until opponent's weapon is at disadvantage or normal against you, just do arena or maps
I can beat tenth stratum 40 5* just fine (as long as no blue or just one using these):
35 Roy
34 Leo
36 Clarine
27 Sharena