I don't have any ceremony ideas...but I would google invitation ideas and there are SEVERAL ways to state on the family invitation that the family will be coming together....

Our family situation is slightly different ...but ours looks something like this:

child number one and child number two request the honour of your presence as their parents

bride

and

groom

unite in marriage...blah blah blah

but in my search to find this...there were several about how they are glad their parents have found someone who makes them happy and are glad to become a family yada yada