Our babes are close together with this coming baby having the largest spacing- 2 yrs 8 months.
I can share what it's like now for us and I don't imagine there being too much of a juggle with the new one.
Our boys spend their days playing in various groupings and having alone time all at their intitiatives. They are all very adept at accommodating absolutely anyone at any age- newborn on. They don't view anyone as outside the possibilities of exploration and play and will ask an adult friend to join in the same thing they've included an infant in.
I think that freelearning is the name I put on what people feel a need to confirm, that our children are doing things that they would put into schoolese. But we're just living, and since I don't know anything different than this, like what it would be like with different child-spacing or fewer or more children, etc..., I don't know anything else and this is as perfect as it can be at this moment and when we need to make changes, we do and will.
If you are hoping for some assurance that unschooling can be done with many littles, then I can give you that, but I only have my own experience to show as evidence and it's us and not you, but I do think that there is no hindrance to unschooling by any sort of child-spacing. We just do what works for us, and I'm assuming you do too, and it would be the same no matter how many dc we had or when they were born.
For us, freelearning is just living, so we live as whatever grouping/configuration we are at whatever time/place.
Do you have specific practical concerns?