From here it seems like actions of ones ancestors do effect the descendent, as G-d says himself that the sin of the forefather is punishable until the fourth generation

This completely contradicts the previous source, saying that children aren't punished for their parents sin, let alone 3rd and 4th generation ancestors

A possible explanation: HaRav Sacks ZT"L

" The first statement refers to Divine justice, “at the hands of Heaven.” The second, in Deuteronomy, refers to human justice as administered in a court of law. How can mere mortals decide the extent to which one person’s crime was induced by the influence of others? Clearly the judicial process must limit itself to the observable facts. The person who committed the crime is guilty. Those who may have shaped his character are not."- Covenant and Conversation

Problem with the solution:

G-d, while giving Chizzuk to Bnei Yisroel al pi Yechezkal/Yermiah, says himself that the solution doesn't work, saying that only the person who sins will die, saying our quote is not true, as only the sinner will die. R' Sacks' explanation that only G-d can give punishment to other generation is seemingly incorrect, as G-d himself says that he won't give punishment to anyone but the sinner

Seemingly, the only time one can be punished for their ancestors sin is by G-d (because we never had said man was allowed to, rather, this Gemara shows just G-d can punish) when the decendent picks up the wicked actions of their forefathers. Can one truly never be punished for their ancestors actions besides for this specific case?

R' Sacks' second solution: Covenant and Conversation

"Rather, what is at stake is the deep understanding of the scope of responsibility we bear if we take seriously our roles as parents, neighbours, townspeople, citizens, and children of the covenant. Judicially, only the criminal is responsible for his crime. But, implies the Torah, we are also our brother’s keeper. We share collective responsibility for the moral and spiritual health of society. “All Israel,” said the Sages, “are responsible for one another.” Legal responsibility is one thing, and relatively easy to define. But moral responsibility is something altogether larger, if necessarily more vague. “Let a person not say, ‘I have not sinned, and if someone else commits a sin, that is a matter between him and God.’ This is contrary to the Torah,” writes Maimonides in the Sefer ha-Mitzvot.[3] "

L'fi HaRav Sacks ZT'L, although one isn't liable for punsihment if his ancestors/realtive wronged and he didn't pick up in his ways, he still is responsible as a relative, friend, neighbor, or many other things for the sins his friend/relative commited. As someone who is close to someone else, it is your responsibility to make sure your fellow is doing the right thing.

We are responsible for our brothers actions. Regardless if we will physically be punished or not, we are responsible for our fellows actions. Although in most cases there is no Ancestral Punishment in Judiasm, one should take responsibility for those around them sins who they couldn't affect positively, and try to influence others to do the right thing, as "Kol Yisroel Arevim Ze BaZeh"