First Question:
The Light - Hex-Sealed Fusion can I use this cards second effect to summon Cyber Twin Dragon The idea i have is to specially summon cyber dragon ,normal summon this junkface and use its second effect.

Second Question:
When a monster says cannot be specially summoned except by fusion above monsters can i still use it? want to use future summon to summon something like Neos Someone.

1st answer:

1. Light Hex Sealed Fusion may special summon Cyber Twin Dragon by tributing Cyber Dragon.
2. This special summon isn't fusion summon, so you don't use LHSF as a fusion substitute monster in this scenario
   
3. In this scenario, Cyber Twin Dragon haven't properly special summoned, so it can't be special summoned from public-knowledge area(i.e monster reborn).

2nd answer:
I don't really get your question, but i'll assume the question is:

Quote:

When a monster says cannot be specially summoned except by fusion summon with the above fusion material monsters can i still use fusion substitute-monster? Iwant to use future fusion summon to summon something like Neos Someone.

if that's what you're asking,then the answer is no,

1. you can't use fusion-substitute monster, when the fusion monster specifically saying their material can't be replaced.
   
2. Also, most card doesn't have an effect while in the deck,so you can't use future fusion and use fusion-substitute monster as a substitute material.
   
3. And...for watever reason(probably because konmai says so), fusion-substitute monster also don't have their "substitute effect" while in RFG

unless stated otherwise any card can be special summoned from non-public knowledge area.
the example for "Stated otherwise" is:

1. Card with "This card can only be special summoned by..." on it's text.
   
2. Card that can not be special summoned (i.e:Light and Darkness Dragon).
   
3. Nomi Monster.(i.e. Judgment Dragon)

yeap that was my question ah so my deck wont work well back to scrap