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 Tomas ay mataba.
Thomas is fat.
Sina Tomas at Julio
= Thomas and Julio
Sina Tomas at Julio ay nandito.
Thomas and Julio are here.
Imbitahin mo sina Marco at Juan.
Invite Marco and John.
Gisingin mo sina Bobby at Dennis.
Wake up Bobby and Dennis.
There’s no need to enumerate all the names when you use the word sina.
Invite Marco (and the rest).
Because you used the word sina, it is understood that there is someone else with Marco.
If you meant only Marco, your sentence would have been:
Imbitahin mo si Marco.
(using si instead of sina)