My kids get home from school very late in the afternoon, almost at dinner time, so homework gets to be a challenge sometimes for us too. At least they are in 2 separate school systems so my youngest has a chunk of time home with just me before her big sister gets home from middle school. We take full advantage of that time the house is quieter without a sibling distraction. It was a lot harder a couple of years ago when they had the exact same schedule. If they had to sit down together at the dining room table, it would never work, it would just be bickering and fighting, too silly, or whatever. They HAVE to have their own space for homework.
My youngest (9 year old) has a snack, and then starts homework right away. Her down time is only 10-15 minutes before starting. 30-40 would never work for her. She also is not allowed screen time before homework. So it's usually a quick snack and a little attention for the dog, and she starts. When the weather is nicer, I'll allow her more free time before starting if she is playing outside, that has never really been an issue, even if it pushes some homework until after dinner.
My oldest gets home so late she doesn't start homework until after dinner, but it's right away after dinner. No TV or video games. I'm OK if she has music or her cell phone next to her. At 9:00, all electronics and music have to go away. That is the goal bedtime for them, it doesn't always happen, but that's what we strive for.
I would say the youngest gets priority alone time with Mom nearby at the dining room table for homework. The older kids should leave the room and find their own quiet separate spaces. I would not keep on them to "finish" but I would just not allow any privileges until it's done. Make it their responsibility to see that it gets done instread of yours. My youngest gets distracted all on her own sometimes, but it really doesn't matter to me if it takes her a half hour or 2 hours. The longer she takes, the less free time for her, and she knows it.