at a distance of eighty kilometres or more, and you do not know when it will end, and you have not intended to stay for more than four days, then there is no objection to shortening the four-rakʿah prayers to two. As for combining two prayers, that is not appropriate for you, because you are not actually on the road; rather, you are settled. Combining is only for the one who is actively travelling. A traveller who has alighted somewhere should perform every prayer at its proper time, shortened; that is the Sunnah.
As for Jumuʿah, it is not obligatory upon you in the situation you have described so long as you do not know when your assignment will finish and you have not intended to stay more than four days, for you are still travellers. However, if Jumuʿah is established in a mosque near your workplace in town, it is better for you to pray with the Muslims, not to stay apart, so that you may obtain the reward. If you intend to stay more than four days, or you know that the assignment will not end before four days, then in that case you must perform the prayers in full—four rakʿahs—and it is not permissible for you to combine, because the basic rule for a resident is to offer the prayer in full, and you are residents, so the rulings that apply to residents apply to you. Allah knows best.
Question: If they were actually in this last situation you have just mentioned—namely, they know that the assignment will not be completed within four days—yet they still shortened and combined the prayers, is anything required of them concerning the prayers that have already passed?
Answer: As we have said, if they know that their assignment will not finish before four days or more, then in that case they have formed the intention to reside, and they are therefore obliged to pray the full prayer like residents. However, if it happened that they prayed and shortened, I do not think they have to repeat those prayers; they are valid, Allah willing. In the future, though, they must not shorten the prayer in such a situation. And Allah knows best.