You can take them both from my understanding as I’m using both right now and getting heals from both sources. I’ve seen my hp dip and blocks come up on screen w/o attacking and my hp shoots back up to full.
Faithful is a healing spell which benefits from healing effectiveness and subsequently triggers Prayer. The benefit from healing effectiveness therein increases the value of Holy Symbol and Valor (though I am finding the latter better for my build since elemental protection is easier to come by).