My tastings policy is "max 6 persons, no children". I figure a max of 6 allows for both sets of parents to attend should they like.
To weed out the rif-raff, I charge the wedding couple $40 (which comes off the bottom line should they place an order) and $10 for each additional person they bring (no credit applied). I always get the tasting money up front regardless of whether they place an order with a deposit that day or not. That way should they cancel, I at least have the tasting fee in hand.
My decision for no kids came about after a couple of "incidents". Once a couple brought their rugrats (3 under the age of 4!!) and my husband and oldest child ended up entertaining them in our backyard. Another couple brought her two hellions that felt like they had the run of my house, inlcuding upstairs and into my kids rooms -- parents didn't seem to care - I was horrified.
Not that parents/in-laws are much better - I can tell you horror stories about them too but I won't go there!
It would be nice to have just the wedding couple only but I don't think that's fair and some brides really need the extra input.
To be honest, I'd rather not do tastings at all but it's part of the biz.