Dvc - presence of respondents in court--is it essential?

Presence of all the respondents is not necessary.

Respondents other than husband may file Application u/sec.205 Cr.P.C. "Magistrate may dispense with personal attendance."

Even if court refuse to allow application of 205 CrPC, other respondents may not appear. Court cannot issue warrant against respondents 

Only husband needs to appear on every hearing.

If the husband fails to attend the court on various dates, what is the recourse as per law?

Either the husband(R1) or the Legal counil has to represent. On the absence of R1, ned to submit the absence petition.

Judge can order for exparte order, if no representation.

In Criminal court both should appear. Allowing petition U/S 205 is Discretion of the court.

cases of domestic violence are quasi civil nature so personal appearance of respondents are not necessary and they can give their appearance through counsel

Amisha ji is correctly observed. Courts have discretionary power and bias is a subject of study in Law itself.