I am a resident of Saudi Arabia working in Riyadh. I intend to bring my family (wife and three children) to stay with me for five months. I would like the month of Hajj to be among those five months so that we can perform hajj. If I succeed in procuring visa for them and they are to come, I would like to meet them in Jeddah so that we can perform Umrah first and then go to Riyadh. My questions are:(1) As we have been away from each other for almost one year, can I sleep with my wife before going to Makkah to perform Umrah? (2) Where do I wear "Ihram"?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

1) If your wife intends to perform Umrah when she visits you in Saudi Arabia, she is not permitted to go past Ihram stations without assuming Ihram for the Hadith that reads: "These places (Ihram stations) are for the people (e.g. coming from Syria al-Juhfa …) as well as for others who pass by them on their way to perform Hajj or Umrah" .
In other words, if your wife enters into the state of Ihram, it is Haram to have sex with her, since this action invalidates your Umrah (i.e. both of you).
Thus, you have to perform Umrah first, and then, you can do what Allah allows you to do (i.e. having sex), since performing Umrah requires only a few hours. And one can and should be patient.
2) You have to enter the state of Ihram at Wadi al-Sail Ihram station, which is on the road coming from Riyadh. But, if you travel by air, then you have to enter the state of Ihram when you come close to any Ihram station. A crewmember on the plan usually announces nearing the Meeqatt or you may ask them. However, you can enter the state of Ihram from your place of residence, although it is better to do that at Ihram station.
Allah knows best.