Install RHEL 7.x with boot envi (BE) and alternate boot envi (ABE) on a same disk

GM Gurus.

I have a typical requirement where I have 240 GB hard disk and I need to install RHEL 7.x on it with boot envi (BE) and alternate boot envi (ABE) on a same disk by partitioning the hard disk into 120 GB and 120 GB. Also Once I install it on one partition successfully on BE I need to sync (mirror) the ABE all the time. If I need any maintenance I need to split the mirror and have updates on BE and if all looks good I need to reattach the ABE.

Can any one please help me with any document/blog that I can refer to or if some one can provide me the procedure that would a great help and much appreciated.

Regards Venu.