Re: Double Birthday Parties
As the pp have said just bring one gift for the kid you know.
I have my kids bdays together (g/b who just turned 3 and 9) on the invites, for the people that know both the kids like family and close friends I put both names on the invite. For my daughter's friends who she wanted to invite I only put her name on the invite since they don't know my son.
When I was 11 or 12, my friend and I had a party together, our bdays are 2 days apart. The party was at her house, it was our friends, and mostly her family, my family didnt live near so only my mom and sister were there for me. We both got gifts, but none of her family brought gifts for me and I didn't think it was wrong, or rude and it didn't bother me at all.