I would suggest a triple set of radio buttons: one for 'in', one for 'out' and one for 'undecided'.

Mutually exclusive toggles is likely to require lots of explanation and could leave the user confused: A pair of toggled buttons seems to offer 4 different combinations (A+/B+, A+/B-, A-/B+, A-/B-) but you are going to need to explain that there are only three (A+/B-, A-/B+, A-/B-). On top of that the third option is never explicitly show in the control settings - in your case you show 'in' or 'out' but 'undecided' is only shown by the absence of any other setting. This too would require further explanation.

A triple-set of exclusive radio buttons should do exactly what you want: all three options are visible and the fact that the user can only select one is indicated by an established pattern.

I would suggest a set of three radio buttons: one for 'in', one for 'out' and one for 'undecided'.

Mutually exclusive toggles is likely to require lots of explanation and could leave the user confused: A pair of toggled buttons seems to offer 4 different combinations (A+/B+, A+/B-, A-/B+, A-/B-) but you are going to need to explain that there are only three (A+/B-, A-/B+, A-/B-). On top of that the third option is never explicitly show in the control settings - in your case you show 'in' or 'out' but 'undecided' is only shown by the absence of any other setting. This too would require further explanation.

A set of three exclusive radio buttons should do exactly what you want: all three options are visible and the fact that the user can only select one is indicated by an established pattern.