Is li'an still possible, and what is the fault of the children now, and will a great tribulation occur if the husband performs li'an despite fatwa number 33617 stating that the children are his and there is no longer time for li'an, and fatwa number 32872 stating that he bears a sin if he does not perform li'an?

There is no contradiction between the two fatwas. The first pertains to a man who knows of his wife's adultery and delays the process of li'an without excuse for a long period, in which case his li'an is not accepted. The second, however, concerns a man who ascertains his wife's adultery and that the child is not his; in this situation, he must promptly initiate li'an, because to abandon the denial (of paternity) while knowing the child is not his is unlawful.