To all Shiromas,
Understand that the name "Shiroma" has other pronounciations. Other ways of pronouncing "Shiroma" are "Gusukuma" and "Gushikuma".
Once way for you to determine if you all are cousins is to find out if you all share the same "yago" or house name.
In England, house names are used. An example is Duke of York and Duke of Edingburgh. In Okinawa, before the Japanese government required that Okinawans adopt last names, all of our families were referred to by house names.
My family, "Senaha" is from Okinawa-ken, (prefecture) Nakagami-gun (county) Nakagusuku-son (village) Aza-Tsuha ("Buraku" or "Block). In Tsuha, we are known as the house name "Mae-Shimojo", not Senaha. There are too many Senaha's in the village for us to know who's who.
Once again, if you can find your house name, you will know if you are cousins.
How to find your house name? Ask any issei or nisei in your family. They might know. Most of the issei in Hawaii's plantations could not read or write. To communicate, they relied on the letter-writer at the plantation store who wrote (for a small fee) for them when they sent letters to Japan. The letter writer always wrote in the third-person (Senaha, Kako-sama wants to send his greeting to all and to tell everyone that all is well on Ewa Plantation, although, he regrets to inform you that his youngest son, Tomozen was killed in action in the Korean War.) The envelope that the letter was sent displayed not only the address but also the yago.
My grandfather's letters to his brother in law had the address printed in English on the face but, "yago Itoman-gwa" was written in Kanji. This told everyone in the village (who could not read English anyway) that the letter is intended for Arakaki, Chogi-sama. The yago system acted as the main system of identification.
Today the Yago system is still in use. My grandmother's family runs a sashimi store in the village and while visiting, I noticed that their customer list (on the wall) was listed by yago, not surnames.
If you read the obituaries in Hawaii you will occasionally find a yago listed in the obiturary of an Okinawan person who died. An example would be "Nakandakari, Kamado AKA Yago nudunchi".
I hope this helps!