Is there a Saint Thais and if so what is she the patron saint of?
Saint Thais is a saint of the Greek Orthodox church. According to the legend Thais was a public sinner in Egypt who was converted by St. Paphnutius, brought to a convent and enclosed in a cell. After three years of penance she was released and placed among the nuns, but lived only fourteen days more.
There is no mention of her being a patron of anyone. Penitents might pray for her intercession, I suppose, and "public sinner" is biblespeak for prostitute.
Saint Clare of Assisi was the patron saint of many things, but the reason why she is the patron saint of embroiderers is because embroidering means stitching cloth in a certain way to make pictures on it and or writing. So, she was the patron saint of embroiderers because she was the one who invented it.
There is no patron saint of siblings. There are, however, patron saints of similar causes. So, for example, the patron saints of families are Francis of Assisi, Joseph, and Maximillian Kolbe. The patron saint of dysfunctional families is Eugene de Mazenod. The patron saint of family happiness or harmony is Dymphna. Finally, the patron saint of family life is the Infant Jesus of Prague.
There are many New Testament saints named David so you will have to be more specific. If you are referring to King David from the Old Testament, they are generally not given the title of saint. King David is not listed as a patron saint. If you are referring to St. David of Wales, he is the patron saint of that country and of doves.
I adopted a beautiful girl from Panama several years ago who is expressing more interest in her heritage. For Halloween, our church is encourage students to come as their Patron saint, so we decided to look up the Patron Saint of Panama. According to Catholic Online the Patron Saint of Panama is Immaculate Conception, Immaculate Heart of Mary
When you were born your parents chose your name and patron saint. Now that you are a young adult about to be confirmed, you have the opportunity to choose a different patron saint. It should be a saint you admire and would like as a role model. The Saints are our role models in the faith, so a person picks a particular Saint for his/her patron.