I think your breeder needs to not say those things, because it isn't true xD
There are a lot of people on this site alone with two or more males, and it's not like a girl boy duo wouldn't ever fight.
If anything, just bring Franklin down to the shelter with you and have them meet there or somewhere else more neutral, if you think that would be best.
Please don't go on sex alone. It really depends on the dogs (and how you manage them). I've had all mixes of both, and have never had a problem. It depends on dominance vs submissiveness. If you have two dominant dogs no matter what sex, they will fight. I have two females that are best friends. But Seanna is dominant, and Sage submissive. Seanna and Jackson are the two that butt heads the most, and they are boy/girl. If you exert your leadership skills as a pack leader, then you won't have a problem. My newfoundland bit my corgi mix once (both boys) when Dillon stuck his head in Sam's bowl as he was eating. Dillon got two staples on his nose, never stuck his head in Sam's food dish again, and they never had another fight as long as they lived. Dogs work it out. That is the only example of blood having ever been drawn in 20 some years of having a mish-mash of dogs--rescues, pets, strays, etc.
We have 3. Aber, the old guy (he's going to be 12 in 3 months) is fine with everyone and everything. Ragnar and Kelso are half brothers and they have the occasional scrap, but it's more sound than real fury anymore. I think it was a testosterone issue. We were waiting until Kelso was a year until we got them neutered, and then he got the mange and had to wait until he was clear before going under anesthesia. Blood was drawn (on Kelso, never Ragnar) on several occasions, as Kelso's face was balding and Ragnar has a big overbite. They fought over toys, food, me, and it seemed to come out of nowhere. The longer they go without their nuggets, the better they are getting. And most of the time now they cuddle and clean each other, and both can now sit on top of me together and there's no problem at all. They'll just fight over toys now and only inside the house.
I agree with the posters who've said that personality probably matters more than sex.
My experience: Before we got our corgi, Lloyd, we had a male shepherd mix (Sammy) who was quite lonesome after the passing of our older pomeranian (Max). Max was definitely the dominant one of the two, so Sammy grew up with someone else being the boss. When we brought Lloyd home, Sammy didn't try to boss the new kid around, and if anything, they both seem to be more or less equals.
I've read some articles saying that dominance theory isn't true/useful/etc., so maybe it's more personality, but since both male dogs are not terribly assertive, they do get along quite well :)