Proof of HUF property

Sir, Father(F)& Mother (M) have 1 Daughter (D1) and 3 sons S1,S2,S3. S1, then married, bought a property with help financial help from F, S2 and S3, 30 years back(S2 and S3 then unmarried). F, S2 and S3 had a family business going with father as proprietor. The title deed and the purchase agreement ONLY mentions S1's name, and no HUF entity or names of F,M,S2 or S3 in these documents, except that F & S2 have signed as witnesses. F & M are no more, and S2 and S3 now claim this is HUF property by virtue of their financial contributions (~10% each) and funds from family business and want an EQUAL share in financial and property benefits of redevelopment. D1 is settled abroad after marriage for >30 years, and has neither contributed to purchase nor is asking for a share now. Does the property qualify as HUF property ? What documents do they need to produce to call it HUF property? How important is the contributions of each member with respect to ownership, even though the title deed is in one name?