I have 2 ssd's in my laptop.. one with windows 8.1 and windows 10. works just fine.
On the second I run Oracle linux 7.0 (more or less the same as RHEL 7) with grub2 on the mbr.
How should I inform bcd to boot linux on the mbr of the second disc?
If it's a UEFI PC, then MS won't allow it, but you can come at it from the other side by calling Windows from grub.
If it's legacy BIOS, you can add a Linux entry to the BCD using EasyBCD.