Combine JH and HS, or keep them separate?

Band:

Pros:
- Larger group
- More instruments covered
- Less pressure

Cons:
- Differing abilities
- Differing maturity



Choir:

Pros:
- Larger group
- Less pressure

Cons:
- Differing abilities
- Differing maturity



Other considerations:
- 2 days or 4 days a week?
- once set, can it be changed?
- jazz band/orchestra/elective?

Edit (3/26/17):

It seems like combining the groups remains the best option for several reasons.

First, the obvious con: there will be a considerable amount of skill difference between younger and older students. The music will naturally be intimidating to 7th grade students and mundane for 12th grade students.

Here's my solution: if 7th graders are completely unable to learn the music, just write an easier part for them. Call it the "7th grade part" where all instruments play the melody in unison, or some variation of that idea. For the 12th graders, combining classes would open up an extra period during the day where I would be able to offer an "Advanced Ensemble" class, open only to 9th-12th grade, possibly by audition only, but require Advanced students to also be in the Concert group. This would allow the students an outlet for challenging themselves and also keep them enrolled in the larger group and provide for a better concert experience for the younger students.

Another reason for combining the bands/choirs is simply the number of students at Dutton/Brady school. Even if 100% of the student body enrolled (which isn't likely in the next five years), I would still only have about 45 students, which is actually a pretty good, average-sized band or choir. Having multiple instruments playing the same part or multiple voices singing the same part would allow me to group inexperienced players with experienced ones, providing the younger students with good role models and someone to help them when they get lost.

On the topic of either two or four classes per week, it seems as though meeting four days a week is impractical. The problem with asking for four classes per week is that I am not allowing the other departments at Dutton/Brady to have an equal amount of time with the students (unless we went to something like 10 periods a day, which won't happen). Therefore, especially with the junior high students, it will need to remain two classes per week. However, I would like to argue for requiring the junior high students to take a full year of band for both the seventh and eighth grades. This would be accompanied by required scheduling of shop, FCS, foreign language, art, etc. so that all of the junior high students would have experiences in all of the electives in order to make a better choice of which electives to take during high school.