Wow, a thread about an issue I actually have experience with, LOL!
First of all...your pictures are amazing! What beautiful boys you have!
I have a mother cat and 4 of her kittens (they are over a year old now) Two boys, two girls. Let me tell you, it has been a real experience watching these babies grow up together!
Yes, they absolutely can have a bond that lasts. As mentioned before, neutering is critical. You must do that before they become competitive and territorial.
My boys are very, very close. Now, they do not snuggle all the time, like they did when they were babies. However, they still greet each other with a body rub and they still groom each other. And they love to play! As adults, they do not tend to like to actually sleep all wrapped up in each other like they used to. Only every now and again, when it is fairly cold. But, they always sleep near each other. Actually, all of the cats usually sleep at least int he same room as each other.
I think the only sort of sad thing I have noticed is that while they still see the momma cat as momma...she treats the boys a little bit different than the girls. She will sometimes groom them a little bit, but for the most part she does not seek their attention anymore and more often that not will snub them when they seek hers. But, with her girls...she is totally the opposite. She will groom them for hours.
I think that when the boys hit a certain age, even though they were neutered pretty young...it's like she sensed that they were males and to keep a distance. I dunno. That is the only explanation I can think of. I know that she loves them and they are part of her clan, but she is just not AS affectionate with them as the girls.
Cat behavior is amazing.
I think your boys will probably always love each other and be best buddies. They may express it in more subtle ways as they age. It's hard to say.
but, good luck with your awesome furbabies!