Two names,
one deed

Point 1The two title forms

Joint tenancy with right of survivorship: equal shares, and the survivor absorbs a deceased owner's share automatically — outside the will, outside probate. Tenants in common: shares in any proportion, each owner's share passing by their own estate plan. Married couples in New York get tenancy by the entirety's protections by default; everyone else chooses between the two.

The choice is really an estate-planning decision wearing a title vest: survivorship suits partners who want each other protected without wills and probate; tenancy in common suits unequal contributions, investment partnerships, and anyone whose share should go to their heirs, not their co-owner. Deeds default carelessly; choose on purpose.

Point 2Unequal money, cross-border wrinkles

When contributions differ — one partner funds 70% — tenants in common can hold 70/30 title matching the money, or the difference can be papered as a loan or gift. Silence is the expensive option: mismatches between funding and title invite gift-tax questions (acute for non-US contributors, whose US gift exemptions are tiny) and resentment arithmetic at any exit.

Cross-border pairs add the estate overlay: survivorship moves a non-resident's share outside probate but not outside US estate tax, and the marital deduction that shelters citizen spouses is limited for non-citizen survivors (QDOT planning exists for exactly this). The title line on a co-bought deed deserves ten minutes with a cross-border adviser before closing — the retrofit costs multiples.

Point 3The co-ownership agreement

The exit clauses carry the document: real co-ownership breakups founder on 'who buys whom out at what number,' and an agreement that names the appraisal mechanism and the clock converts a crisis into a procedure. New York's default remedy — a partition action forcing sale through the courts — is the alternative everyone should be drafting to avoid.

Point 4Lenders, boards, and the practical layer

Financing jointly means joint liability: every borrower underwrites, every credit report matters, and one partner's debts price everyone's loan. Co-ops interview all buyers and weigh combined finances; some resist non-occupant co-owners (the parent-co-signer structure meets board policy building by building). Condos take co-buyers as they come.

Insurance, taxes, and records want one operator: a shared account funding the monthlies, one partner administering with visibility for all, the basis worksheet tracking both contributions. Co-buying doubles the humans and should not double the administration — it should split it on paper that survives the partnership's weather.