What happened in this situation?, would they have abortions?, would they get another job?, would they their hide their children and pretend they didn't have any while they were working?

All of the above. I’ll be talking about prostitution in general because oiran is just a very subset of women. Just to be clear, the oiran was a euphemism for popular prostitutes in the specific quarter of Yoshiwara, the yūkaku (pleasure ward) of Edo. There isnt much use of this word outside Edo referring to the similar people, other than that this word referred to female courtesans of the Kyō. I think it is best to consider oiran Japanese idols in the modern sense because they lived sterilized lifestyles, but under heavy restraints.

Abortions were quite normal for prostitutes and those working in the ‘sex industries’. There were a number of concoctions that worked like the modern abortion pill. In addition abortion was quite normalized due to the various economic situations. Infanticide happened during famines in the Edo period. There were different methods of birth control also. I am just pointing that it does seem rather easy to control or manage pregnancy based on population dynamics during the Edo period.

Generally should a prostitute go through pregnancy, they were not allowed children with them. They usually had the grandparents take care for however long. Grandparents often raised children. That is not to say there was never any children growing up in brothels because there were according to death records and physical evidence (graves of children) around brothels. Some did leave once pregnancy occurred. Some times it in fact planned that many prostitutes would often marry their regular customers. There were various strategies for getting out of prostitution because prostitutes were generally indentured meaning sold in debt.

I was surprised by how accepting the Japanese culture is of prostitution, or some kinds of prostitution at least

Just extend the answer a bit. Japanese culture is probably more tolerant of prostitution. I think tolerance might be the better word because there is a stigma about prostitution and especially oiran such that Confucianism or Buddhism had these puritanical morals like elsewhere, but justified it differently. Prostitution was tolerated because it was a consequence of the Tokugawa peace and the economic institutions. Essentially prostitution boomed in the Edo era because of indentured servitude or using labor (or buying people if one looks at it that way) as credit. Wives and children had a status of quasi-property and required subservience to the head of household (father/husband) under the ie (household) system. The household system which was a product of Confucianism (ruism), or at least Japanese interpretation of it, allowed this. So in bad economic times children and even wives could be indentured should it be necessary for household survival whether it was taxes, private debt, or not having resources for winter or the next harvest. It didn’t even really need to be last resort. But yet it was allowed because prostitution was considered justified as filial piety. So indentured prostitution had paradoxes of morality and economics. Some prostitutes were very independent and this upset the patriarchy. So this might be the target of stigmatism rather than the morality of prostitution. The oiran were particular visible targets of puritanical ire. On the other hand, economics (money) and politics was also a heavy influence. Brothel owners were big tax payers and the authorities often used them as intelligence agents.

For an in-depth post see here

Sources

See the above link.