Ihram of someone on a business trip

Q: We are members of Armed Forces who participate annually in the Hajj mission for a period of one month and stay at Al-Shara'i`. We form guard alternating groups in a place far from the camp while some of us do not take a shift and remain on standby for any emergency. We hope that you, with the help of Allah, will inform us on how those remaining behind in the tents should perform Salah (Prayer). Should they combine and shorten Salah, or not? Moreover, there are Masjids (mosques) in some camps where some want to perform Jum`ah (Friday) Salah. Furthermore, Jum`ah Salah is held in a neighboring district, may we perform it with them?Also, while on the mission we set out as a caravan and are not allowed to stop at the Miqat (sites for entering the ceremonial state for Hajj and `Umrah). We, therefore, pass the Miqat to Al-Shara'i`, a place outside Makkah. May we then go out to Al-Ji`ranah to assume Ihram there, or return to Al-Sayl Al-Kabir to assume Ihram, as we have passed it while on our way? Or, should we assume Ihram from the place our camp is located, i.e. Al-Shara'i`, a place only a few miles from Makkah? (Part No. 11; Page No. 141) Sometimes we go on missions to Al-Madinah Al-Munawwarah. We spend ten days or less at Al-Madinah, and then move to Makkah Al-Mukarramah where we also stay ten days before returning to Al-Madinah once again. Near the camp of this brigade in Al-Madinah there is a stationary camp wherein there is a place to perform Jum`ah Salah. May we perform Jum`ah Salah there? Please, inform us soon, may Allah reward you well! We hope that you will deliver us the fatwa in writing as we differ on the issue of how to perform Salah every year. We ask Allah to guide everyone to what is correct. As-salamu `alaykum warahmatullah wabarakatuh (May Allah's Peace, Mercy, and Blessings be upon you!)