I think that only two intensity lines will be visible. The reason being that we can write the probability amplitudes like this: A_1*[observed] and A_2*[observed-1]. Where [observed] gives either 1 or 0 (observation of a particle or not), and [observed-1] gives the opposite by default. This makes it so that we can write the intensity as I = |A_1*[observed]|^2 + |A_2*[observed-1]|^2 + A_1* * A_2 * [observed] * [observed-1] + A_1 * A_2* * [observed] * [observed-1]. The only values that can be found are |A_1*[observed]|^2 and |A_2*[observed-1]|, sins [observed] * [observed-1] always gives zero. This means that there are no interference effects and only two lines will be visible.