Just based on that, I would consider using the brown buck (larger) as the potential herd sire for a number of reasons (excluding the dairy aspect as you didn't mention that as an important aspect):
1. First and foremost that has to be based on his temperament. If that's good, the rest will hopefully follow.
2. He'll be about the same size as the does, so easier breeding/kidding and similar sized offspring.
3. He looks "meatier" than the tan buck, so if meat is a desire, that would be beneficial. He's much stockier than his 1/2 brother from the pictures provided.
4. Since to my understanding, 4H kids and shows is about showmanship and therefore you don't need to have purebred animals, so the offspring can be used. However, I also believe that shows require the goats be de-horned, so the kids produced (or any animals to be used) would need to be either polled (born hornless) or dis-budded shortly after birth. You would have to check/double check this.
5. By my understanding, bottle babies are much more docile and people friendly than those that are dam raised. Though this is NOT cast in stone, it seems to be the consensus. (tough subject, not trying to cause a fight) Therefore, you should plan on removing/"pulling" all kids as soon as they are born, before they see mom and vice versa, so they will bond to humans rather than mom, and so they all don't scream bloody murder when you eventually do remove/separate them. Of course this means more work for you, as you are now "Goatie Momma" and will now have more than the three you already have, to worry about... they'll need to be fed, and you'll need to milk the actual momma goat to get their food.
If dairy is a consideration at all, you might want to consider buying does that are dairy breeds. If dairy is not a huge concern, and meat is, then you'd most likely want to focus toward meat breed does. Crosses of Kiko, Boar, or Meat Master goats (primarily pure meat breeds/crossbreeds), and there are others. If you want both meat and dairy, you can look for crosses between the above and (full sized) Nubian, Lamancha, Alpine, Sannen, etc. Or minis of any of the above (pure breed crossed with a Nigerian Dwarf buck or Pygmy buck). Nigerian Dwarfs have one of the highest butter fat contents, Sannen's usually have the highest production (gallons). So much to decide.
I mean a book could be written just about this subject, right? I've gone through all of this myself trying to determine which/what would work best for me! There's so much info available here on the site and so many with years of experience that can provide information, guidance, help. And all have their particular favorites
... but really, I mean, all you gotta do is ask
Just by reading through some of these threads between now and the time of eventual decision making, you'll be able to form opinions based on your own experiences and what you've learned/heard/read.
Edit to add: Both bucks and the pup are very handsome (or pretty for the pup)! I really like the color of the tan buck.
