The Tagalog word sina is the plural form of si. It's what grammarians call a "personal topic marker." In Tagalog, you must use either si or sina in front of proper names.
Si Greg ay mataba.
Greg is fat.
Sina Greg at Julio
= Greg and Julio
Sina Greg at Julio ay nandito.
Greg and Julio are here.
Imbitahin mo sina Marco at Juan.
Invite Marco and Juna.
Gisingin mo sina Bobby at Cliff
Wake up Bobby and Cliff.
You don't even have to enumerate all the names.
Imibitahin mo sina Marco.
Invite Marco (and the rest).
Because you used the word sina, it is understood that there is someone else with Marco. If you only meant Marco, your sentence would have been:
Imbitahin mo si Marco. (using si instead of sina).