あぐらをかくは
to sit cross-legged や
to sit with one's legs crossed flat in front of you
と言えます。
to sit with one's legs crossed だけだと椅子などに座っている時に足を組んでいる意味にもなるので、flat in front of you をつけたほうがあぐらをかいているのがわかりやすいと思います。
My father-in-law often sits cross-legged in the Tatami room in his house.
「義父は家の畳の部屋でよくあぐらをかいて座っている。」
My back isn't very good so it's hard for me to sit with my legs crossed flat in front of me for very long.
「腰が悪いので長い間あぐらをかいて座るのが辛い。」
ご参考まで!