Yes, they are. Wash them well, and consider peeling them if it's not too much trouble.
Yes, fruits and vegetables are kosher for Pesach. If cooked, they need to be cooked in Pesach vessels, and if canned, they need certification of being kosher for Pesach.
Yes, it is.
No.
It would have to say "Kosher for Passover" on the can.
"Pesach same'ach" (פסח שמח) or "Chag Pesach Same'ach" (חג פסח שמח).
Kitniyot refers to a subgroup of food items that are not eaten my Ashkenazi Jews during Pesach. If those items are certified kosher then they're kosher.
Legumes are kosher for Pesach, however, they belong to a group of foods called kitniyot. Legumes fall under this category as they have a similar texture to chametz. The ban on kitniyot applies only to Ashkenazi Jews.
Pareve kosher for Pesach margerine is available at kosher butchers and some supermarkets that stock a large Passover inventory.
An Orthodox rabbi who is trained in kosher supervision can help
No, phyllo dough is chametz and cannot be used during Pesach.
Kosher for Pesach (Passover) food is marked as such on the package label. Markings include a P incorporated into the hechsher, the words 'Kosher for Passover' in English, and 'Kasher l'Pesach' 'כשר לפסח' in Hebrew.
Yes, grape seed oil is kosher for Passover for all groups including Ashkenazim. You would have to check the labeling for a valid Pesach hechsher though.
There are brands of kosher for Passover baking powder but they have to be marked specifically for Passover.