Not medised 3 months is youngest age shown on pack. I think the saline nose drops are ok because they are a bit like tears iyswim I have just checked pack I have at home and doesn't say anything about age at all (assume it would if there was a lowest age for use). But would recommend googling to be sure.
Regarding the vicks, snuffle babe, baby olbas oil etc. I don't think any problem with a bit on a hanky near DS. I used to put on a tissue and put it under DDs mattress, at the head end of her cot.
Also, sitting with them in the bathroom with shower running until it is nice and steamy in there.