You can not mark the other mummy without unmarking the first. The Divine Challenge specifically says "The target remains marked until you use this power against another target,..." I will assume you still decide to mark the other mummy, to give it a reason to come to you rather than pester the others.
20 damage to spider from Ngeri. Next one to hit it before Ngeri's next turn can spend a healing surge and gain +5 hp.
15 damage to mummy 1 from Grimnir. Grants CA to Grimnir on his next attack.
8 damage to mummy 1 from Grimnir.
Mummy 2 regenerates 10 hp.
Eitri, Ráslím and Cáï's turn. Don't forget to roll saving throws
http://www.tangveje.dk/pbp/asod/grids/spidercave7.png
C: Cáï - Init 31, 37 hp, 8 tmp hp
S: Spider - Wounded, cursed by Grimnir, marked by Eitri, immobilized and -5 attacks until end of Ráslims turn, CA to Ráslím until end of his next turn, next to hit before Ngeri's turn can spend surge+5.
Er: Ericr - Init 25, 60 hp, +1 defences*, +2 damage, +4 regen while bloodied, 8 tmp hp, can't use second wind
N: Ngeri - Init 24, 18 hp, 8 tmp hp
G: Grimnir - Init 24, 52 hp, darkspiral aura 2 pts, 8 tmp hp, +1 defences*, +2 to one d20 roll before end of next turn
1: Mummy - Bloodied, Cursed by Grimnir, Challenged by Ericr, CA to Grimnir on his next attack
2: Mummy - Wounded, Marked by Eitri, Cáï's Quarry, Cursed by Grimnir
Ei: Eitri - Init 19, 47 hp, +1 defences*, 8 tmp hp, restrained + vulnerable 5 necrotic
R: Ráslím - Init 9, 32 hp, immobilized, +1 defences*, 8 tmp hp
* Ericr and all within 3 sqaures of him gain +1 to all defences.