The pension paid from the government to your nephews is their private property, and it is lawful for anyone of them, if they are adults and consent, to include their share of the father's pension in the partnership and contribute to the shared living expenses. However, for those who are under age, their guardian's consent is to be sought regarding mixing their pension and sharing living expenses with the uncles after considering the minor's interest. This applies to the rest of the holdings that (Part No. 14; Page No. 306) the children earn or inherit, each according to his/her property.
The partnership shall include living together, investing, decisions, and benefits by their consent and choice. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.