If I have more than one Solosis on my Bench, does Solosis' "Mini Link" attack do +30 for each of them?
No, you only get a maximum of 30 more damage regardless of how many Solosis are on the Bench.
Source: Fates Collide FAQ (2016-05-05), TPCi Rules Team (2016-05-05)

Relevant cards

Note: All applicable cards may not be listed below.
XY10_33