Game Point

[MarkG]

Your visiting MIL will definitely give W resentments towards both you and MIL. IMO you and MIL should not be having dinner, although there are both good and bad sides to this:

good:
W will hopefully realize she's messed up in the head because MIL sees it
WAS's run until they run out of places to run.... burning bridges can shorten the distance they put between you
children could also aid in pointing out the above since they see W's and MIL's relationship go downhill over you

bad:
W could develop resentments toward both you and MIL
giving W more reasons to have resentments will definitely hurt your sitch if you want to R
children might become confused about family structure and what happens in a separation or divorce

If it were me I'd stay away but bring the kids and have talks when you do, but not stay for dinner. I could be wrong, but it just seems like too much contact.