As you have mentioned :”So basically if i had to take hayz and janabah ghusl together…”
Let me please make this clear also that while it is allowed that man can have relation with his wife just after her hayz has been stopped and she has not yet done her Ghusl e Hayz but it’s better not to be done and woman should take her Ghusl e Hayz then she she can have relation with her husband.
Ruling 457. If a woman is divorced after her ḥayḍ has stopped, the divorce is valid even if she has not yet performed ghusl. Furthermore, [after her ḥayḍ has stopped but before she has performed ghusl] her husband can have sexual intercourse with her. However, the obligatory precaution is that intercourse must take place after washing the vagina; and the recommended precaution is that having sexual intercourse with her should be avoided before she has performed ghusl. However, other acts that were unlawful for the woman during ḥayḍ on account of them being conditional on her being in a state of ritual purity – such as touching the writing of the Qur’an – do not become lawful for her until she performs ghusl. Similarly, based on obligatory precaution, acts that have not been established as being unlawful for a ḥāʾiḍ on account of them being conditional on her being in a state of ritual purity, such as staying in a mosque [also do not become lawful for her until she performs ghusl].