Answer
(Fatwa: 357/357/M=1431)
(1) It is not necessary.
(2) After doing Umrah if you return before beginning of the month of Shawwal, then Hajj will not be fardh on you only due to performing Umrah. And if the month of Shawwal starts there and you own the expenses of Hajj, then it will be fardh on you.
(3) If Hajj has became fardh on you already, then perform Hajj and during it you can perform your Umrah as well.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband