Cody and I are Mr. and Mrs. Trans in our church (which has a relative large trans community) and TG support group. I do know of at least one other transman/transwoman couple - I met them recently at a TG support group for FTM and their spouses - I went there last month with Cody and I met the other couple.
I have seen FTM/MTF couples at least twice in youtube documentaries about transgender people. One was two teenagers, and the other one was two people somewhere in their 30s or 40s.
I also know of a couple that's a transwoman and a genderqueer that goes to our church.
Same thing with Cody and I. Neither of us lost a spouse to get to where we are, and we're both the same age - he's one month older than me.
One nice thing about being in a trans/trans relationship is that we (usually) don't have to worry about mis-gendering, although I have heard of trans/trans couples getting into arguments and than mis-gendering each other. But it is really nice that Cody sees me as a woman, even if he sees me with my wig off, 5:00 shadow, or naked. He is the only one that will ever see me like that, and I am looking to the day that my beard and 5:00 shadow is completely gone. He still sees me as a woman even though I have the wrong parts.