They will breathe. And they will breathe whenever it makes sense to them. Assuming they are conducted, the conductor/director may ask them to breathe in certain places and/or not breathe in other places. In between those, they often will intentionally stagger breathe, which isn’t half and half. Instead they will each try to breathe at their own time and quietly.
The best thing to when writing for voice, winds, brass, and strings is decide when you most want singers and players to definitely breathe or recharge the bow and when you don’t want them to.
You can write in symbols like slurs that indicate not to breathe or recharge, and you can write in rests or breath marks to encourage them to breathe or recharge when it makes musical sense to you. Singers and players are used to seeing a mix of these in music and they work very hard to not breathe or recharge when it’s not good and to breathe or recharge when it is.
If you care when they breathe or recharge, then give them guidance. If you really don’t care, then they will decide for you.
In terms of learning how other composers handle this, the best two options for you are to learn to sing or play these instruments and play or sing in ensembles; or to do score readings with close listening and see how players and singers deal with it. Ideally you would do both.