Hi Amy!

이 문장들 재밌네요

재미있어서요.   Because it is fun.
재미있었어요.   It was fun.
재미있었어서요.   Because it was fun.

pronunciation is different each other.
있어서요 => [이써서요]
있었어요 => [이써써요]
있었어서요 => [이써써서요]

오늘 재미있어요.  Today is fun.

어제 재미있었어요.   Yesterday was fun.

그때는 재미있었었어요.   At that time, it had been fun.

The translation is correct. Be careful about word spacing.

재미있는 여행이에요.  It's a fun trip.

재미있는 여행이었어요.  It was a fun trip.

재미있는 여행이었었어요.  It had been a fun trip.

The conjugation is correct.

이 문장들 재미있네요.

재미있어서요. Because it is fun. (It's pronounced like '재미이써서요.)

재미있었어요. Because it was fun. (It's pronounced like '재미이썼써요.)