After the storm I hosed down the patio to clean it off (the) branches and leaves(the) leaves (that had fallen there).

Or: “to clear off the branches…”

I once travelled with a group of pensioners and felt very alienated fromby their music tastetaste in music.

“Alienated from” tends to be in connection with a group of people or a community, however implicitly. Example: “She felt very alienated from the Reform movement.”

“Alienated by” would make more sense here, but the meaning is slightly different.

I doubt that he can carry the project forward alone,; we have to take on new staff to support him.

The two clauses can stand alone as independent clauses, so we need an appropriate conjunction or punctuation (period, colon, semicolon, depending on the situation) to separate them. In some situations, a comma may be acceptable, but that’s only when there is a strong stylistic relationship between the clauses.