
CountofUndolpho |

If I'm unsure about such things I usually think is it a benefit with a cost? if so I 'round up' otherwise I 'round down'.
In this case grappled is a detrimental effect, it restricts movement so take the worse interpretation i.e. no TWF when grappled.
Personally I would say that would be across the board even for head butts and knees etc, flurry being the only exception. You are supposed to be at a disadvantage when grappled, countering that disadvantage should be 'expensive'.
If I find myself arguing round the houses for an advantage I haven't paid for in feats and skills etc. then, usually, I'll assume I'm wrong - when I calm down!

Tarantula |

Using two weapons not necessarily requires two hands, it is not like blade boots are not iconic enough. Not sure what is the surprise.
Agreed. If your weapons don't require both hands to use (such as blade boots or unarmed strike) then TWF away. If you want to use weapons in hand, no dice.