Hi, welcome to the forum, seller is correct, 1st is ww2, 2nd is ww1.
ww2 m26 adrian has an original liner and paint apears correct, front photos are needed.
ww1 m15 adrian needs more photos, but so far looks good.
From the pictures they both look good to me.
The WWII has the 1937 style badge fitted whcih often has a slightly different color, there are many reporductions of these, but this one looks alright.
The WWI from the outside looks nice, do you have a picture of the liner of the WW1 helmet?
I don't like the look of the liner, this could be a repro, also on the corrugated aluminum strips looks wrong.
But do you think the two shells are original?
Yes I do.
The M.26 looks right but the beige liner is actually 50's dated.
The M.15 has a reproduction liner as said.