If the firms are different there is no conflict of interest. Wife and husband are distinct entities under law. 

Both can bid separately in same tender both have separate identity 

it is not ground for disqualification 

Yes. If concern authority does not have any issues.

Both the husband and the wife are proprietors of their own firm respectively.

Therefore there is no restriction nor conflict of interest if both are bidding separately in the interest of their respective firms in the same tender.

There is no legal infirmity in it. 

Yes, certainly. Both tenders may get rejected for this reason.

- Since, the wife and husband is running their business under two different firm names , it means that both are responsible for the dealings of their own firm separately .

- Further, the two will enter into an agreement with the bidder separately towards their respective firms , hence the wife and husband both can quote in the same tender. 

Dear client,  Husband and wife are two different identity under the eye of law.  So both of them can compete for the same tender and this is not a ground for disqualification unless the rules set for valid tender so provides

Yes they can if there is no conflict of interest