I think you answered your own question.

I haven't a clue, but I love the way you asked!
Wikipedia says:
A traditional 3-letter monogram has the initial of the individual's last name (surname) set larger, or with some special treatment in the center, while the first name initial appears to the left of it and the middle name initial appears to the right of it. For example, if the individual's name is Mary Ann Jones, and Jones is the surname, then the arrangement of letters would be thus: MJA, with the surname initial set larger in the center, the M for Mary to the left and the A for Ann to the right.

Married or engaged couples may use two-letter monograms of their entwined initials, for example on wedding invitations. Married couples may also create three-letter monograms incorporating the initial of their shared surname. For example, the monogram MJA might be used for Michael and Alice Jones. However, monogramming etiquette for the married couple varies according to the item being monogrammed. Linens, for example, typically list the woman's given initial first, followed by the couple's shared surname initial and then the man's given initial (AJM).

I am now more knowledgeable!

I would go with JTB. With the T being stitched almost twice the size of the first name initials.
Making the centre point of the letters all in a line so that the top T is slightly above and the bottom of the T is slightly below the other 2 letters.

What you listed as the way you think it should be JTB is correct.

I agree.

Well, I agree with you and a lot of others. Hope it all works out. Love Chris