她们一起正在一起吃早饭。

她们俩穿一件着蓝色的穿着衣服，很漂亮。

桌子上有一杯咖啡，一瓶果汁和一些/一盘食物。

Because you use some quantifiers for coffee and juice, I think it's better to use them for food too, and it sounds better in Chinese. I think it's better to say "桌子上有一杯咖啡，一瓶果汁和一些/一盘食物。" or "桌子上有咖啡，果汁和食物。" . "桌子上有一杯咖啡，一瓶果汁和食物。" is grammatically correct, but it's a little bit weird.

我觉得她们在一来这家饭店、是因为桌子和椅子这里的桌椅又新又好看。

Did you want to say they come to this restaurant because the tables and chairs here are new and pretty?

她们俩穿一件着蓝色的穿着衣服，很漂亮。

桌子上有一杯咖啡，一瓶果汁和其他食物。

我觉得她们是在一家饭店、因为桌子和椅子又新又好看。