to suggest that DFIL and DMIL keep their

[bruceb]

.....newly-discovered Christian beliefs to themselves a bit more?

There's a lot of history that is too boring to go into here, but they have just started going to church after many many years of steadfast agnosticism (is that a word?).

It just seems a bit off that they are now getting all 'religious' when the kids are around...... harrumph

I can see your perspective (and there's not too much info in your OP to be more perspicacious than this)but, from their perspective, their new found faith may be so important to them they want to share it with those whom they love, ie, your DC I appreciate your view though, just trying to colour in what your ILs may be feeling, iyswim?

When people discover something new that they think is great it's normal to get rather evangelical about it.

That is particularly apt in this case

I think you need to smile politely and let it all wash over you.