Eibbed, my kids are older so take my advice with a grain of salt, and we are also not homeschoolers in the traditional sense, but we do a bit of part-time homeschooling with all three of our kids. All three are very different in terms of ability, needs, interests etc - and my two dds in particular are highly prone to distraction over what the other dd is doing. What I do is to have a game plan for each of them, so that when one is working all three have "work" to do - and it doesn't have to be school work, it could be something that is a cleaning "chore" (which was fun for my kids at 4), or a quite play activity. The key is that I have a list for each and they each need to check off what's on their list.
I also make sure I have something interesting and fun included on each list, so it's not all "work".
polarbear