All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
(i)
Required number of ways 
(ii)
Number of ways for both brother are in team 
Number of ways for both brother are not in team 
Required number of ways 
ways.
(iii)
We consider three cases here.
1. Remaining midfield plays as midfielder
2. particular midfield plays defender
3. particular midfield not playing
Required number of ways ![= {3 \choose 1} [{8 \choose 4} \times {3 \choose 1} + {8 \choose 3} \times {3 \choose 2} + {8 \choose 4} \times {3 \choose 2}] {5 \choose 4} = 8820](https://theculture.sg/wp-content/ql-cache/quicklatex.com-6b641ccddaec4c86366670a9cef4592f_l3.png "Rendered by QuickLaTeX.com")
ways.
Personal Comments:
Students can solve (ii) by consider two cases, i.e., midfield bother is in team while attacker brother is not and midfield bother is not team while attacker brother i. (iii), I was a bit lazy to type it out to many times so I simply factorise everything, knowing that the number of ways to choose goalkeeper and attackers are the same.
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