Do merry and Haruhiro get together?
It becomes increasingly evident that Merry has feelings for Haruhiro in volume 9 and onward. Volume 10 ends with her attempting to tell Haruhiro that she loves him before she dies. Through extraordinary circumstances, Merry is revived in Volume 11, much to Haruhiros delight.
What happens at the end of Grimgar of fantasy and ash?
The season ends with Merrys past behind her and the surviving heroes coming to terms with the life and death nature of their time on the world of Grimgar.
Does Ranta like Yume?
Yume. Yume and Ranta have a complicated relationship. However Ranta does seem to care about her, quite possibly even liking her as shown by him being upset with Haruhiro when Shihoru is mistaken in thinking Haruhiro and Yume are together.