Involving Grandparents with Names

We have had boy and girl names picked since before we even got engaged lol our first boy we said we'd name Logan (a combo of Long and Megan) and our first daughter would be Magnolia.

Problem: Grandpa doesn't like Logan. He keeps suggesting Alexander. We told him as a compromise he may name the children their Vietnamese name which will be their middle name. But we are choosing their first/American names. I gave him a few ideas of patterns for the Vietnamese names I wanted him to stay within. But he shut them down saying the meanings were "bad" (meaning your child would grow up with a tough life). And kept suggesting Alexander Truong Phung. I hate the name... without a doubt I will not name my child Alexander because I want Logan. But even the Vietnamese name I don't want, but at the same time if I do not give him something he wanted I feel they'll never let me hear the end of it... 

Also, can we make note that he hasn't even thought of a girl name? We don't know the gender of our baby yet because our party is in June but is he that confident it's a boy? Because I honestly think it's a girl...