If multiple grafts are 'in line', then they all are part of the same path (a single line) to the roots. Grafts 1 and 2 are always in line with other grafts, since there is no other way to the roots. Grafts 3, 4 and 5 are in line
with 1 and 2. But grafts 3, 4 and 5 are not in line with each other.
Draw a single line from any graft through the tree to the roots. All the grafts that you connect with the line are in line.
Multiple grafts similar to what I show have been done successfully. Technically, there is no limit to the number of grafts. In the practical sense, no more than three or four in line grafts are done. Usually, it is just one.
For grafts that are in line, only one graft can be done at a time, usually on a yearly basis. Grafts that are not in line with each other, i.e. grafts 3, 4 and 5, could all be done at the same time. And yes, since 3, 4 and 5 are not in line, you can have several different kinds of apple on one apple tree.
Grafts are weak points of structural strength in the tree. You will want to be sure that grafts like 3, 4 and 5 are whip grafts. Grafting is a skill, so don't be discouraged if they don't take the first time. You will need to read up on it from a reputable source. FYI, 'in line' is my personal description for clarity. As far as I know, there is no universally used designation for such graft groupings.
