A book by Peter N. Carroll titled "The Odyssey of the Abraham Lincoln Brigade" can be viewed online. There are several passages pertinent to The Convulsionaries, the Young Communist League, and the International Workers Order, and the individuals united therein.

Here is one.
The subject is an African-American named Vaughn Love.

"In 1932, a Communist rally on behalf of the Scottsboro Boys attracted his attention, and he started to work selling subscriptions for The Liberator, the newspaper of the League of Struggle for Negro Rights. Later, he joined the International Workers Order, a Communist-led fraternal organization that offered cultural programs. Among the IWO's activities was Harlem's "Suitcase Theater," in which Love helped form a group of interracial entertainers known as the "Convulsionaries." Their vaudevillian shows delighted left-wing audiences by blending ideology with satire. When news of the International Brigades reached the IWO, Love and his white cohorts eagerly pressed to enlist. "
--page 41 in Chapter 3, "Awakening in Hard Times,", in Part I: Causes. from The Odyssey of the American Lincoln Brigade.

On page 186 in this same book, author Peter N. Carroll identifies the four members of the "Convulsionaries" specifically as:

Ernie Arion
Vaughn Love
Harold Melofsky (spelling of last name varies)
Bernard Abromofsky, who was Harold Melofsky's cousin

The original post in this thread references the archives associated with Miriam Sigel Friedlander, and her ALBA brother Paul Sigel who was killed in action in 1938.
I could be mistaken here, but in my reading of Carroll's text, Paul Sigel, while an ALBA soldier, was NOT a "Convulsionaries" member, only on friendly terms with his fellow ALBA soldiers who were members of the group.

In my quick perusal of Carroll's book, I find:

Arion was the first to be killed in action.
Melofsky followed within months.
Abromofsky, frightened when the fighting and killing started, deserted more than once; when he was arrested and brought back to the battalion, one disgusted officer shot him in the head, killing him.
Vaughn Love survived and was still granting interviews about his experience as a veteran in the 1970's.