Reb eliezer
“What about davening a hoiche shmonei esrei (saying a loud shmonei esrei) ? We say kedusha together and start shmonei esrei then 10 people will daven together.”
The OP’s question is when we don’t have 10 people davening together “I came to a shul where there are 5 people who want to daven,”
The Shevet Halevi says davening WITH the Shatz is Tefila Betzibr. Applying it here (which he doesnt do he is discussign a guy who came late but it seems comparable) would mean They DON’t Daven silently rather the shatz starts “chazaras Hashatz” and the Tzibbur joins him.
1) This wouldnt work for Maariv
2) By shacharis, we don’t generally do “a hoiche shmonei esrei”
3) By mincha standard practice by “Hoiche shemoneh esrei” is the Shatz is quiet after Atah Kadosh, in which case it seems they wouldnt have tefila betzibur. (I suppose he COULD say the whole thing aloud)
So in practice the Shevet Halevi has little bearing in this question
As to the original OP
“If people who are struggling to get a minyan call me to come,….”
why is joining them a “chessed” If there is someone bed bound or a chiyuv or something I hear . But if its just a bunch of people too lazy to go to the shul that has a minyan davening, why is helping them daven beyechidus (according to most poskim) a chessed? If you want to do chessed offer them a ride to the big shul