Honestly I would recommend just using the 10 gem revive (if you haven't already) to get by the last stages. I had to use it on faimon 5-7 using 4* fire hellhound, 3* water fairy, 3* fire vagabond, and then subbed in 5* guildies evo'd monsters. If I remember correctly you get 10 gems for beating the last lvl so it only cost 20 gems total. All my summons only had +5 and 6 runes, mainly 1* and 2*.
Now if you want to beat it legit w/o revive with the summons you got.. idk, probably just lvling priest, fairy and warbear to 30 would make a pretty nice difference, but it still may not be enough. 5-7, since they are non-elemental summons, can be pretty rough. You got better summons than I had though for sure, so it shouldn't be to hard that really.