Say, $M_1=\left \{a^n:n\,\,is\,\,a\,\,multiple\,\,of\,\,2\right \}$

$\overline{M_1}$ will be strings where n will not be multiple of 2

So, both $M_1$ and $\overline{M_1}$ are infinite. So, $L(M_1)=T_{yes}$

$M_2=\left \{a^n:n\geq 0\text{}\right \}$

$\overline{M_2}=\phi$

So, $M_1$ is infinite but $\overline{M_1}$ is not. So, $L(M_2)=T_{no}$

So, $T_{yes}\subset T_{no}$ as $M_1\subset M_2$

So, it is a **non-monotonous **property. Hence **non-RE**

Correct me if I'm wrong