First: a family-like bond =/= actual family. This is an important distinction.
There's this thing in psychology called the Westermarck Effect, in which being raised in an actual family environment produces a severe desensitization to any sexual attraction. This is why you do not find your sister or brother attractive, and additionally why kids who are adopted at an early age into a family generally do not find their siblings attractive either.
This serves an important part in this argument - the "family" dynamic that a lot of you are talking about that would be "weird" if the Toa got together seems to be rooted in this idea that they would be an actual family - which would be weird.
But in reality, this is not an instance of members of a family that have grown up together developing a romance between them. This is a group of similarly aged young people who have only just begun to work together and become friends because of their situation. They are also thrust into incredibly similar trials and are given responsibilities that only they can really identify with.
This does not necessarily mean that a romance has to happen among them. They can still remain platonic. However, I don't subscribe to this theory that it would be "weird" for it to happen between two members of the team. It's actually extraordinarily realistic for two people who can relate to each other and have to spend a lot of time together to develop a romantic relationship - time actually makes people appear more attractive to each other.
If you have ever had a group of friends in high school that all hung out platonically, and then two of them within that group got together, you'll know what I mean. Time makes people closer, it makes relationships stronger, and many times it will turn friends into romantic partners (hence why so many people say when they're engaged "I married my best friend".) Good friends becoming romantic partners is an extremely common occurrence and happens all of the time in real life.
I'm not sure how being busy with saving Matoran conflicts with becoming closer with a teammate and having romantic feelings for them. You still build relationships even though you have a "duty" on hand. It would be akin to saying that the Toa can't be friends with each other, because they're too busy to have friendships. They are capable of both at the same time.
People in the military often (extremely often!) have loved ones at home - not just family, but specifically romantic partners (girlfriends, boyfriends, wives, husbands). I think it's very possible to be part of an elite military force and still be capable of romantic feelings.
Friendship makes the Toa more human, but romance wouldn't? They're both extremely relatable human emotions. A good romance is really just an enhanced, more deeper and personal friendship.
This is essentially why I talk about this at all. It's this idea that I'm directly wanting to combat here: that romantic love is evil, or useless, and that it doesn't add anything to a story and we must keep it away at all costs.
I thoroughly believe that romantic love is intrinsically a core developmental part of human interaction. You grow to know another person intimately, develop further bounds of empathy, compassion. communication and maturity. It changes you and matures you, even if it ends badly. Anyone who's been in a relationship can point to what they've learned because of it, be it flaws in themselves or flaws they should have seen in others, or both.
And when I'm developing a character, as the character writes itself and we see the interactions in the story, I don't think we should approach with this eight-year-old cooties mentality that romance is gross and just ruins everything because it's icky and boring.
Romance is a mature avenue for character development and growth. That doesn't mean it always needs to happen. It just means that there's no actual reason to eliminate it as an option entirely.