It's a bit tricky to get these
feel accurate, since they are represented in weight but it makes more sense to think of them in sq footage
or smth.
A thick reindeer hide could be heavier than a seal-skin which has almost no hair
to compare, even when covering smaller area.
Having said that,
I'd put grey seal skin way above 10 lbs - closer to bear's 18 or elk's 24lbs. Big grey seals can be as much as 2,5 meters long and weigh over 300kg / 660 lbs. (Avg female 1,6-2 m; 100-190kg; wikipedia)
20lbs sounds nice and round like the seals themselves
5lbs of grey seal skin... luckily none of the grey seal grandmothers don't know about this. They'd be turning in their abyssal graves...
Ringed seals would be smaller on average than reindeer skins, but close. Maybe 6-7lbs.
Calves' skin sizes are quite debatable.
In real life: The new spring calves are really small, but grow quickly during the year. First autumn skin would be about third to half of an adult skin size - a year later almost adult skin size. So basically anything below that can be considered 'right' - the calves' graphic does look quite small though. (EDIT: I made a sug about
calves.)
Adult animals' skin size varies too - sometimes substantially - but I won't get into that now. It's fine.
Btw, I was aware of the slight difference of grouse family skins. But I haven't met a single bird skin (swans and such included) that was much bigger. Added 'about' in my second comment.