1) office is justified in asking for succession certificate . if will is produced probate is necessary as far as house is concerned nominee is only a trustee for all legal heirs . on your wife death . her mother you and your child have 1/3rs share in house .
2) if in laws have produced will and notice served upon you then you have to oppose grant of probate as will is forged and fabricated .
3) if no nomination is made in pf account then you would need succession certificate to get provident fund dues
4)Section 39 of the Insurance Act says the appointed nominee will be paid, though he may not be the legal heir. The nominee, in turn, is supposed to hold the proceeds in trust and the legal heir can claim the money.in your case you and your child have claim on said proceeds received by your in laws . you should file claim within period of 3 years .