1 If wife is one of the witnesses .Is this weakens the case.?
It depends. That is why care should be taken to produce the list of witness and only those witness which would be useful should be produced before court.
2 If the 2nd witness is tenant .Is there any problem?
(But actually the 2nd tenant was testator 's personal assistant.The opposite party is explaining him as a tenant.)
Let the opposite party address the witness as anything. There may not be a problem if the tenant is a relevant witness.
3 The opposite party is writing that the application for grant for probate is not in accordance with the provisions of section 276 (1) (d) and section 276 (2) (a) of 8ndian succession act.what does it means?.
They are quoting the relevant provisions of law to dispute your case, your lawyer may give a strong counter to that issue.
4They are also explaining that testator was mentally not well and for myself that i am a ill minded person (which is 100%false) should i hv to present any document or evidence in this regard and when?
This is a matter to be discussed during argument, you can apprise your lawyer about the relevant facts who will take care of the situation.
6 They are writing that testators sinature is shaky and space is different letters .Have they to any proof in this regard?
The burden of proof is on their shoulders, let them prove their allegations.