Assisting disabled family member: eligibility for benefits on ILR?

My brother has been seriously ill and became disabled as a result of his illness. He got ILR though and because his illness is stopping him from returning to work, is he eligible to go on universal credit?
If he does apply, does that bar him from applying for citizenship in the future?
He is currently receiving funds from me and another family member to pay his bills but we can't afford to keep paying sadly.

Now that your brother has ILR he is no longer under Immigration Control. Therefore there are no restrictions for claiming Public funds. This won't affect a British citizenship application.