Can a single squadron for example a single A Wing engaged with 5 Tie fighters prevent all 5 Tie fighters from moving?

Yep.

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While a squadron is at distance 1 of one or more enemy squadrons, it is engaged with all of those enemy squadrons.
• An engaged squadron cannot move.

Each individual TIE Fighter is engaged with the A-Wing, so each TIE Fighter cannot move.

This doesn't work for squadrons with the Grit keyword, which lets squadrons moved if they are engaged with only one squadron (YV-666s, Lancers and Scurrgs are the only non-uniques with that).

However that A-Wing shouldn't last long against 5 TIE Fighters.

Also keep in mind, obstruction blocks engagement.