Seirin would be the protective team in that ‘only we can mock and tease them’ way. Like I think Kiyoshi and Mitobe would be completely chill and supportive and treat them like precious little angels in love. Izuki and Koganei would make some silly innuendo at them every once and again. The freshmen trio would be a bit taken a back, because they still bicker and poke each other whenever the team is out somewhere, but they can also be seen sharing glances and hugs etc. Hyuga would be a bit on the fence at first, but eventually accept it because what can he do about it? And Riko would be torn between being the hardass coach she is, and not taking any romance bullshit and being enamored because they are so cute and she is not so secretly weak to cute things.
And because of making her confused she would make them run extra laps and then even more laps when they come back holding hands.