No, no , no... DON'T worry! I think you are jumping the gun.
He is only 7.5 months old! Also, DO NOT compare the twins... each child/baby is different.
Talking speed and ability does NOT have anything to do with "intelligence" or "smartness." Einstein did not even talk until he was 3 years old. Many "geniuses" had this trait, Mozart too.
MANY babies don't even talk until AFTER 1 years old... with boys, it's often even later. DON'T pressure the poor child.. or yourself. EACH baby/child has their OWN unique personalities and abilities and develop differently....
Really, this is too early to "expect" your son to "talk."
I have 2 children. My eldest, my girl, was "talking" before 12 months old. My 2nd child, my son, is almost 24 months old... he is advanced in many areas of development... and is bi-lingual, and very cognizant of anything that goes on. HOWEVER... he does not yet "talk" as is "expected" at his age. No big deal. Sure, at this age he is now, I had him assessed... there is NOTHING wrong with him. My son is very selective about what words HE "chooses" to say... he is very precise & analytical...and the words he does say are quite impressive. One of the first words he said for example was: "help" and "more." Not mama, or dada...but the word "help"... which attained for him a lot of goals he had in mind. The Speech Therapist also said that ANY syllable they sound out IS "talking"... it's just not our "adult" way of expecting it to be. She said my son is very bright.. and he seems to CHOOSE what and when he wants to talk...and his understanding of the spoken word is advanced for his age. So, they do not call his "talking" "ability" a "problem."
Also, your son is making "screaming" noises, and saying "ah" and sometimes "ma." THIS is called "pre-talking." Remember... talking is also a development... not a spontaneous occurrence in which they suddenly exclaim perfect wording all of a sudden. Whether we notice it or not... any noise, babbling, sing-song sounds they make etc., THIS is called pre-talking... it is them getting ready, and practicing sounds and moving their mouth & tongue, and experimenting... as long as your son is doing this, then that IS appropriate. THAT is what my son's Speech Therapist said.
*You may also teach your babies "baby sign language" already. I will help them and you, to communicate even before the are talking. I did that with both my children. It's great and fun.
Anyway, they also say that boys just talk later. I would not worry. Appreciate the differences in your twins... each has their own time-line, personality, abilities, and unique qualities and temperaments. If the twins are always compared... it could turn into a "habit" that will just stigmatize them later and just be negative for them. Celebrate the uniqueness of them....each strength can compliment the other, and they will then learn to be close with each other, instead of fostering competitiveness or insecurities between them.
All the best,
Susan