Kosher Grape Juice

Sure you can. You can even mix the wine and grape juice - it's usually what I do. If you have a little wine low in alcohol and use a small cup, it should be allowed.

I do not see why not.

Sure. You can still use grape juice instead of wine ... is the fruit of the vine, after all.

And, many people abstain from wine for many reasons.

ive drinking wine since my Millah brit so if I was allowed eight days, I do not see why not:) chag Sameach ve Kosher