Usual Ta In Advance My Trusty Solvers,

[Godeye]

6a) Soprano’s target, maybe, capturing current theme? (5) t-----
12a)Large family member goes to welcome British crew (9)----e---
18) Raises squad to cross river nearer its source (8)
7d) Left instruction involving gown in motel, say (11,4)--r--------/---d

[Mamyalynne]

5 Topic - Top C round i(symbol for current)

[dannyk13]

6a.Topic

[Toorak]

6 tenor

[Mamyalynne]

7 Portmanteau Word

Left - Port
Gown - Manteau
Instruction - word

[Lie-in King]

6a Topic - 'i' (elec. current; symbol, in) 'top C'
12a Tribesman - 'B(ritish)' (in) 'tries' (goes) + 'man' (crew)
18a Upstream - 'ups' (raises) + 'team' (to cross) 'r(iver) '
7d Portmanteau word (mo[tor ho]tel, say) - 'manteau' (gown, in) 'port (left) word (instruction)'

[Mamyalynne]

18 Ups t R eam

[Toorak]

Ignore mine :-)