I love both these names (they're both on my favorite names list) but I'd never use both because in the legend, Tristan and Isolde were lovers and so it just doesn't work.
Other combos that don't work in the same manner:
Arthur and Guinevere
Lancelot and Guinevere
Paris and Helen
Romeo and Juliet
"Chan eil tuil air nach tig traoghadh"
Capt. Malcolm Reynolds - Half of writing history is hiding the truth.
- Serenity