I think most of those are usable, really.
I'd avoid using Gladys, Thelma, and Mabelline.
Gladys and Thelma are still a bit too dated. Mabelline I'd avoid because of the makeup brand Maybelline, not that it's not a lovely name. It's just one of those things.
As for Betty, if Elias had been a girl his name would've been Beatrice nn'd either Birdie, Betsy or Betty. So, that's my route.
Hazel : I like it, it's very usable.
Luella : A bit of a tongue twister, I don't think it's very usable.
Nellie : I named my favourite cow at my grandparents' farm this when I was a child. So I like this name :)
Della : I prefer Nella which is more usable in my opinion.
Mabel : I would say it's dated but I know a little girl with this name, she can't be older than 4. Definitely a brave choice.
Mabelline : too close to the makeup brand.
Gladys : not very usable.
Thelma : brings to mind Thelma and Louise, so not very usable in my opinion.
Opal : a brave choice, but why not :)
Constance : Well I find it usable but I'm french and it's not unusual in France. It might be more so in an english-speaking country.
Elva : not very usable.
Betty : I find it old-fashioned, but to each their own. My favourite way to get to the nickname would be good old Elizabeth.