You are right. Okearinasai means welcome home or welcome back. Listed below are usage examples for "welcome aboard" in Japanese. Getting on your bus: Welcome aboard! = ご乗車ありがとうございます！(Gojosha arigato gozaimasu) ladies and gentlemen, welcome on board, and of course welcome to Boston. = 皆さま、ご乗車ありがとうございます, そしてもちろん、ボストンへようこそ。(Minasama, gojosha arigato gozaimasu, soshite mochiron, Boston e yokoso) Getting off your bus: Thank you for using AA bus. Have a good day. = AAバスをご利用いただきありがとうございました。それでは良い1日をお過ごしください。（AA bus wo goriyo itadaki arigato gozaimashita. Soredewa yoi ichinichi wo osugoshi kudasai.) I hope this may help you.

Just say: go jyosha arigatou gozai masu ( go, Joe share, alligator, go that I math )

In Japanese おかえりなさい has mean "I'm glad you back to me/here safety." or "I got you just back here." or "I missed you. I was waiting you back to" and all. So you can say Okaerinasai おかえりなさい in Japanese, when someone just came back to you or your place. ^-^

If you are talking about tour charter bus, you have many times getting on and off of one group. For first time of getting on time, usual greeting words is enough, I think. Like, "ohayou gozaimasu" (=Good morning) "konnichiwa" (=Good afternoon) "konbanwa" (=Good evening) Also "Boston e youkoso!" (=Welcome to Boston!) Then after above, after they return to your bus from some sightseeing, you can say "okaeri nasai" (=Welcome back) Anyway, if you make mistakes, they appreciate your Japanese words, become closer with you. Don't worry.

Welcome on Board on my bus today : Your driver ” :　Honjitsuha Gojyousha itadaki mashite arigatou gozakimasu / Thank you for boarding Today If your guide : Honjitsuha Goriyou itabaki mashite arigatou gozaimasu/Thank you for using us Today. Short by driver : Gojyousha arigatou gozaimasu Thank you for boarding all ok to use Short by guide : Goriyou arigtou gozaimasu /Thank you for Using