Hello,
If your m.2 SSDs are of a new generation, for achieving the maximum performance you will need a card adapter with x8 PCI-e interface, as a single m.2 SSD uses 4 PCI-e lanes. On the other hand, an m.2 device is perfectly capable to achieve 1000MB/s, so your system may not be able to fully utilize the speed of a single device, let alone a pair of them.
Also, you must assure your motherboard supports booting from a PCI-e device. And, equally important, with the addition of a x4 or x8 PCI-e m.2 adapter, your GPU may lose x8 PCI-e lanes (it depends of the motherboard though).