You are not strange to be worried at all!
When we travel and have to board dogs and have someone check in on the cats, we are calling constantly to see if everyone is alright.
You are doing the right thing by having someone come in to check on them. They will feel much safer in their own environment!
Just make sure you leave all emergency numbers should the need arise and leave the number of a relative or another friend should something (heaven forbid) happen. Unless you have your cell phones with you, it's very difficult (and expensive) to reach someone on a cruise ship. This way, you know if anything happens, someone you trust can be there to help with vet care and decisions.
And have a wonderful time! I simply enjoy cruises and cannot wait to go on our next one!