I'm trying to figure out what's wrong with this following Turing machine which determinate that the following language
A=$\{\langle M_1,M_2,M_3 \rangle : L(M_1) \cap L(M_2) \ne L(M_3)\}$ is in $RE$.
I said that we can build a Turing machine that run all inputs in lexicography order,in parallel:
For an input $x$:
we run it on $M_1$ and $M_2$ if one of them rejected the input, we skip this input, and don't use it.
If both of them accepted:
we run $x$ on $M_3$ if it rejected we return $true$, if it accepted we skip this input and don't use it.
If we are in infinite: both $M_1$ and $M_2$ are in loop for checking $x$, or one of them accepted and the other in an infinite loop, or $M_3$ in infinite loop for checking $x$, if we reached this part, so the machine is infinite loop.
What is not correct? I accept if I reached an $x$ which satisfies the condition or I'm in infinite loop.