Who can evade?

Can units not the immediate target of a charge also evade, say because they are behind the charge target and might be caught in a later pursuit (and be unable to evade then)

No, you have to be the subject of the charge (the target) to be able to evade.

If a unit is uncovered by the initial evade and becomes the defacto target of the charge then it can evade but not if subject to a pursuit.

The general rule is you cant react to a reaction - so if someone charges from your front projection you can react even if you were not the main target, however as Zippee points out, you cant react to a reaction so you cannot evade a pursuit

in acase of a Large Unit with T in front and FP in the rear, that is being charged in front by a CP ... the T can evade instead of defensive fire retreating through the FP unit...the CP attacking stops in FP clash ? and FP is not disrupted by T retreating i guess, full interprenetation...

A Large Unit is considered just one unit, even it is composed of two or three normal sized units. It reacts as one. Besides in a unit as you describe (FP+T) the FP are the front troops with archers behind (but the firing is still counted from the large unit front).

A different situation is when you have a GROUP of units where the front is a T and the rear a FP. If charged the T can react (but not with an evade as it cannot interpenetrate the FP behind). However, if you are the active player you can shoot and protect the T. See the example in 5.11.1.1 from the rules.

Why can the single stand T unit not evade? 5.11.1 (2) states the T units can interpenetrate and be interpenetrated by most troops types (including FP.) In 5.12 T units are allowed to Evade in response to a charge declaration. Seems straightforward to me.

My mistake there. When evading they go through almost anything!