How are the Gummi Bears related to each other

We simply never get any information throughout this TV series about family relations between the gummi bears of Gummi Glen or facts about other relatives. But some breadcrumbs can be combined concerning time line:

Nearly all gummi bears were displaced across the sea by the humans beeing jealous of their advanced knowledge, and only a few remained to call the others when it is safe to come home again (mentioned in "Light makes right"). These gummi bears hide from people, therefore no human beeing have seen a gummi bear for about 500 years (mentioned in "The magnificent seven gummies"). That this period can be devided by 100 is confirmed by the appearance of Gummadoon, a great gummi city hidden by magic which only appears every 100 years for one single day (mentioned in "The knights of Gummadoon").

Over the centuries the number of remaining gummies decreased and most of their former settlements are nowadays abondoned (mentioned in "Up, up, and away" and "Day of the Beevilweevils"). And the six protagonists of this series are the last descendants of the gummis of Gummi Glen.

But we never get to know, how old they are or even what is a normal life expectancy of a gummi bear! Therefore we can not estimate, how many generations of gummis have lived in Gummi Glen since the gummi's exodus.

The sequence of the gummis concerning age is easy to guess for the younger ones but tricky for the adults. Zummi and Grammi were favorite schoolmates and therefore may be nearly of the same age (mentioned in ""Little Bears Lost"). When Grammi went to school, Gruffi was a baby and Tummi was not even born (mentioned in "Gummies Just Want To Have Fun").

German viewers may think that Grammi and Gruffi are a couple, but this misbelief is based on a mistake in the German synchronization: One time Grammi quarreled with Gruffi and said to him angrily "I'm goin'" to point out, that she is not of his opinion and will go with the other gummis (in "Zummi makes it hot"). But in the German version, this very sentence is translated with "Ich verlasse Dich", which means "I leave you!".

It was never established. They live like a family but their relation never got stated. It only indicates that they are sole survivor of Gummi Bears race and live together hiding from humans. And as story progresses it never looked important either.

In reply to [1]: http://de.gummibaerenbande.wikia.com

This is excellent factual information, however as a long time fan and followed of the show/ comics/ etc in the US from childhood the relationship seems to be a bit different than mentioned.

As grammi and Zummi were schoolmates, it seemed that they are the eldest and long time companions who at one point were a couple or have such a strong friendship that they are inseparable. Gruffi is Grammis’ younger brother and Tummi is the younger brother of Zummi, but younger than Gruffi (it is possible that Tummi is a nephew of Zummi from unknown parents). Tummi could also be an unrelated adult who was possibly at one time partner or an offspring of an unmentioned Gummi (possible a daughter of Gruffi or Grammi- but not the two together). He definitely gives off the fun uncle vibe to the kids. If doesn’t seem to be clear if Sunni and Cubbi are brother and sister, cousins, or if one is related to Grammi and Gruffi and the other to Zummi and Tummi. My personal belief is that they are children of either Grammi and Zummis’ offspring of Gruffis’ offspring- Gruffi having lost his partner for whatever reason and contributing to his grumpiness as a manifestation of depression. To summarize Grammi and Gruffi are brother and sister, Zummi was Grammis’ one time partner (you can see affection between them occasions, but Grammi is past breeding years and they have a comfortable loving roommate type relationship- their children having moved on in one way or another leaving the kids behind for safety reasons to be raised by their parents/ extended family). Gruffi is either a lifelong bachelor or lost his wife one way or another, and if there were children they have moved on, being close to Tummis’ age). Tummi is Zummis’ much younger bachelor brother and has always been looked after by grammi as if he were her own (alternatively but much less likely he is Zummis child from a prior relationship and when Zummi and Grammi got together Grammi loved him as her own). Cubbi and Sunni are children of grammi and Zummis’ children, or less likely, children of Gruffis’ children (perhaps one of each making them cousins instead of brother and sister). The middle aged adults all having gone off in search of the great gummis or captured/ hiding/ have passed on with the exception of Tummi, and later Gusto (about tummis age or slightly younger/ same peer group) and other discovered Gummies.

It was the 1980s, when single moms and alternative family structure became more accepted and common in Society in the US and the ambiguity allowed children to see their own families in the family structure of the Gummis regardless of the specific situation, IMO