How politely should I speak with my Japanese family when I visit?

Question:

I'm visiting the Japanese side of my family in a few weeks. This includes my grandmother, aunt, and three cousins, which are my age and older. I spent many summers there as a child but the last time I saw them was when I was 16 which was 7 years ago. Up to that point, we spoke in a casual manner, especially with my cousins (i.e. "nanka tabeyou!" instead of "nanika tabemashou ka?").

My question is, as an adult that hasn't seen them since childhood/adolescence, should I continue to speak to my family in a casual manner (i.e. taberu), or should I speak with the standard long form (tabemasu, "desu" form, etc).

Also, I will be meeting other, older family members I probably met once when I was very small. Should i speak standard long form (i.e. ikimasuka?) or should I speak extra politely (i.e. irasshaimasuka?)

(Sorry if any of my Japanese is incorrect, my Japanese is only okay.)

Answer:

You can talk to your cousins in casual form.

On aunt and grandmother, talk to them in "standard long form" (But we do not call it that way in fact).

You don't need to use "extra polite" form because it's mainly for business use.