Hi Yoghurt,
I'm just getting started with SnGs, but I'm pretty sure - re your point 2) - that you can't ever just call if you are in the push/fold stage. I.e. if you are in the right stage of the tournament to be using the push/fold charts then, by definition, you shouldn't be calling anything.
"Example 1- 1st rebound chart: I am on the BU with A9 suited and i have only 6bb left. The CO pushes allin for 13bb. Do i call or fold here?"
You push or fold here and the decision which, is based on stack size, number of opponents etc. e.g. It makes a difference whether you're already in the money, or in the bubble etc.
"Example 2- Rebound chart in the big blind: Do i call with A2 off suit an allin of the small blind for 8bb?"
As above; you don't call. You only push or fold. And which depends on your stack size vs SB and your positoin in tournament etc.
Generally, you are going to need really good cards (at least QQ+, maybe K,K) to justify going allin with 2 other players allin. At least one will likely have a very good hand. Equally, you want to stay out of the way in such a situation as one of the players who went all in will probably be going out of the trny - which is a good outcome for you - with no risk.
Can't help with your q. about whether charts work for larger SnGs. Do you mean MTTs? I expect the priciples are similar but someone more knowlegable than I should advise.
Glatt,
Tim