That's the usual approach. Almost no one puts down double-thick subfloor in residential applications (for cost and handling reasons), and both layers need to be fastened to joists. Only thin underlayment can be fastened just to the subfloor.

I'm not sure what your question about tile means. Subfloor can and should be fastened to joists regardless.

You can probably use a sparser fastener schedule on the first layer, then go whole-hog on the top layer. That would require adequate penetration into the joists, of course.

NO!

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No you should not attach them to the joist and no you should not have them match the pattern of the initial subfloor.

Disclaimer: I take subfloors way more serious than the average human or contractor. I will answer this question but must confess my deep distain for OSB - unless the house will be carpeted. However I am OK (not happy) with OSB in other installs including floating vinyl types.

Your first layer of wood, OSB in this case, is your subfloor. Subfloor should be nailed directly to joists (duhhhh where would you nail it!).

Any other layers that you add is an underlayment. You should not attach underlayment to joists (yes there are cases you would be these are one-offs and not here).

Any scientific study done by (building science, the APA, whoever) will show you that if you attach both to the joists you are building in fact a "swaying floor" in that the pieces will sway with the joists during seasonal changes. By offsetting the underlayment you are deflecting the sway from the joists and allowing the underlayment to move with the subfloor, which should be less noticeable than the subfloor moving with the joists.

So if I am installing OSB subfloor:

1. I would really think about starting out with 1/2" plywood (or my go to 3/4"). Plywood is better and holds nails and screws better for underlayment. But if dead set on OSB make sure you have the tongue and groove on yours so you can lock them together.

2. First layer (subfloor) should be staggered as you would when drywalling horizontally. You can start your edge in the corner but your next row should start at halfway point of the first piece in the first row.

3. I am explicitly not talking about fasteners as it depends on materials AND what the joists are made out of.

4. Felt paper (15lb) or similar material should be used as a buffer between subfloor and underlayment.

5. The underlayment (in your case the second tier of OSB) should be offset from the subfloor. I know there is a recommendation of more than 6" but I would rather just go halfway again.

6. The 2nd layer of OSB should not be attached to joists. Like I said this causes the most seasonal deflection - let's just call it sway. What does sway do? Over time it loosens up your fasteners and creates random gaps between subfloor and underlayment (your layers of OSB). These gaps to you means a squeaky or squishy floor.