Is’t it mad?! I need to do more, like maybe go into my brothers kids etc but even when I’ve done my friends charts they’ve been like, “oh, my moon is X and my mums sun sign is X!” It’s so weird, you have 12 signs in the zodiac, the chances are your signs would be different, not the same popping up. So interesting to me!
And yes - sorry - I just noticed earlier you asked about Retrograde Planets in your birth chart and you’re right, it’s really uncommon to only have 1, or none, when you consider that currently from 22nd Jan to 21st April this year we have 3 month window where no Planets are Retrograde, so all babies born during that time will have no Retrograding Planets in their birth charts. That means all babies born in the other 9 months of 2023 will have at least one, but this in itself is a fairly large window this year so is more than usual! And I would say having only one is probably just as rare as having none - maybe even rarer?!
It’s hard to calculate exact % figures of likelihood, as every year is slightly different, but in my opinion, it’s more common for someone to have the Outer Planets as Retrograde as they Retrograde pretty much annually and for longer periods - so in all likelihood, the most common would be, Neptune 
Uranus 
Saturn 
and Jupiter 
with the Outer Planets, but again, its unusual to be born in a window where only 1 is Retrograding and they tend to Retrograde around a similar time.
It’s really hard to place Mercury 
in the line up because it Retrogrades for 3 weeks, 3- 4 times a year but I would say it would be the next likely, followed by Mars 
and Venus 
Most people have at least 3 Retrograde Planets and it’s more common for them to be Neptune Uranus and Saturn - like mine 
all Retrograding in Capricorn 
when I was born.
It’s a good sign, that you only have 1 in Retrograde, because that means generally you are less inclined to blockages 