Hi and welcome to nameberry.
Your daughter will have two lovely brothers named Travis and Tristan and therefore you were looking to keep the Tr theme for your daughter. I think that with your sons you have chosen fairly traditional names and they work well together. If you choose Trinity I think that the tryndiness of the name spoils the trio a little.
I feel that Felicity Jade would make a lovely fit eg Travis, Tristan and Felicity. Don't you feel that it has a lovely feel to it?
If you were to say keep a T theme then there are some great names for you to select eg
Tessa I think she is instantly likeable
Tamara is a gentle name, fully of feminity and sweetness
Talia or Tahlia is an especially good modern choice, it is unusual but recognised and is a lovely feminine name which I prefer to see after having two brothers.
Tamsin (the feminine form of Thomas) is unusual and semi unisex, as is Tegan but neither of these would be my choice.
Thea is a lovely choise too and very classic
I am sorry to hear that you have been getting some grief on nameboards but hear on nameberry we always try to give you good advice. I hope that you can understand where I am coming from and please let me know if you like Felicity Jade.
Hi, I don't mind Trinity but agree that Tristan and Trinity are too close. What are their nns? Might make a difference.
Tristan, Travis and Tracey? (or Tracie)
What about using the T but not the TR?
Tristan, Travis and Tara (Tarah)
Tristan, Travis and Taren (Taran)
Tristan, Travis and Terentia
Tristan, Travis and Teresa (Tess for nn)
I disagree with many of the others as I think it is fine to go,with Tr beginning for a sibset. Just be careful with that if you plan more more children.
I do like Tristan. Tristan comes across as preppy to me. Travis seems like a very different style than Tristan as it comes across as very country and Southern. Trinity fits more with Travis though I tend to think of Trinity as urban, religious, recent immigrant.
I think if you are going to use Trinity, it works better with a more traditional, feminine middle name like Jane rather than Jade.
Other Tr names that might work, Trish, Tricia, Tracy, Trudy, Truly.
You could also go with T names: Tessa is beautiful.