Of course, you have to make the best decision you can for you and for your son. There is no way to tell whether or not he will wean while you are gone. Many children would after a week-long separation. Some go back to nursing like nothing ever happened. Despite what everyone is telling you, there is no way to know ahead of time what your son will do. You have to decide if it is a risk you are willing to take.
I do have some thought about travelling with a baby...
1. Get a sling or other style baby carrier, and you will not believe how easy it is to travel with a baby. I wore my daughter while travelling out of DIA, and it was great. Between her, my toddler and my mother, she was the easiest one to keep track of! For a 7 month old, a wrap, Ergo or mei tai are great, comfortable options.
2. If you want to keep nursing when you get back, you will have to take a breastpump and pump regularly. This means that every 4 hours or so, you will have to stop doing the tourist thing, find somewhere quiet and private, with the proper electric outlet and a sink to wash at, and have some kind of cold storage for your milk (unless you are going to pump & dump). By contrast, if you have your son in a sling, you can just latch him on wherever you are and keep going about your traveling.
3. I don't know how needy your son is, but he might adjust better to travelling with you than he would to being without you for a week.
4. Since this is a family trip, you will probably be able to get some family members to keep your son for an evening or two while you go out with your husband, so you can still get some quality adult time in alone with your hubby.
5. The sibling rivalry arguement is, quite frankly, silly. When I have to take my baby somewhere and her sister doesn't get to go, I just remind my toddler that the baby needs Mama for milkies. Then I remind her about all the other stuff she gets to do because she is a big girl. If she doesn't like it, that's okay. That is just how things are. I'm explaining to my toddler, not asking her permission. You are not going to set your sons up for a lifetime of rivalry if you decide to take the baby with you!
You will have to figure out what the best decision is. No matter what, I hope you enjoy your trip.
Best of luck,