Hi, C.. Well, the old wisdom says that kids who walk early will talk late, and that definitely seems to be the case with your two boys. On top of that, boys usually talk later than girls and have slower social development, including conversation.
Some kids don't feel the need to talk much until later in life. The fact that he is responding to what you say and also asking for what he wants shows that he's not hearing impaired, and it also shows that he understands how to relate to adults and his environment. I wouldn't worry at all about the fact that he's not a chatterbox. Trust me, at some point when he does start talking a lot, you'll long for the days when he was quiet. LOL!
If you still want to stimulate him to talk more, try teaching him songs with lots of words. Sesame Street is good for that. When you see a bus, try singing the Bus Song "the wheels on the bus go round and round," etc. Make sure you point out things around him and repeat the names of the things. You can even make up songs for the two of you to sing. Kids sometimes sing better than they talk. That should stimulate his speech centers in his brain, espectially if he gets rewarded with attention from you and Dad or Grandma.
That's another thing. If Grandma wants him to talk more, get her working on the issue herself. Get her to sing to him and pay him special attention by talking about stuff he sees in the environment.
Everyone has to be patient with him, though. Otherwise, if he feels anxiety about his talking, he'll take it to mean that there's something wrong with him, and that will either make him shut up altogether, or it will give him fears that he doesn't understand or need to have at all.
Make it fun, with no pressure, and everyone will enjoy the process.
Peace,
Syl