100% правильность не гарантирую, т.к., на мой взгляд, предложения однозначно расположить нельзя. Вот как бы я сделала.
Dear Aunt Flo,
We`re in London and we are on this amazing boat now. After the boat trip we are going to eat fish and chips.
We`ve seen lots of interesting things in London. We`ve been on the London Eye. It was fantastic.
See you soon,
Love from, Al