Thank you for having me when you had three kids of your own to take care of at the same time.
Thank you for being so kind to me when I stayed with you. I know it must not have been easy, especially when you had three kids of your own to take care of as well.
ーThank you for having me when you had three kids of your own to take care of at the same time.
「自分の３人の子供を育てている時に私を受け入れてくれてありがとう」
three kids of your own で「自身の３人の子供」
to take care of ... で「…の世話をする」
ーThank you for being so kind to me when I stayed with you. I know it must not have been easy, especially when you had three kids of your own to take care of as well.
「あなたの所に滞在した際、とても親切にしてくれてありがとう。特に自分の子供３人の世話もあって、大変だったと思う」
I know it must not have been easy. で「楽でないに違いなかったと思う」＝「大変だったに違いないと思う」
ご参考まで！
カナダ 
