As with all birds, they might or might not get along due to different personality types. Especially if they're not of the same species -- it is possible, but not as frequent, and as Suns are larger, the Pineapple could be hurt if they get into a tussle.
Both being very young helps the odds, as does paying close attention to when and how they try to set up their "pecking order".
My birds don't get along with each other. Well, Rosie and Scooter do, but:
Rusty and Rosie are both alpha types.
Scooter is placid and shy.
Tybbi is independent, but has picked up some of my vocalizations. Still, she's not clingy like how Scooter and Rusty are... Rosie isn't clingy of me, and hates to be touched by anybody, but will do tricks (her own free will) for the sake of making me laugh and feel better.
Rosie hates Rusty
Rusty hates Rosie
Scooter likes Rosie and Rusty
Rusty likes Scooter
Tybbi hates them all
Rosie is indifferent to Tybbi, but the others eventually act territorial and aggressive - even though their cages are close to each other.
In their own cages and separate, they all act like a flock, eating and preening at the same times. It's only when they are out of their cages when problems can ensure, so I don't allow that.
But Scooter is 3 years older than Rosie and they got along - it took a couple months of observation and how they interacted, giving them treats along the way.
But if you introduce the two and they start fighting, talon to talon, beak to beak, it's probably a fantastic idea to separate them ASAP and not let them anywhere near each other - for their safety.
Oh, the best way to get them to befriend each other - that I've found, anyway - is via having them meet in a neutral area, where their cages and toys cannot be seen. That removes territorial aggression from the list of possible problems...
As long as you spend time with each bird individually, they won't resent you. Scooter and Rosie have been in a cage for years, and Rosie - who had been effectively rescued from a very abusive situation - continues to warm up to me, in part due to seeing Scooter's acceptance of me and opening up.
