If both your names on the deed and you file a joint tax return the the two of you (or more accurately your joint tax return) are really seen as the taxpayer for that property because it is reported on your joint tax return. 

It will likely be easier to get acceptance of a more accurate appraisal with support from a performing lease.

The minimum distributions you take and report on your income tax returns have to be based on the values reported by the custodians to IRS, so it's important to be accurate.

For a more accurate financial projection, factor in these additional expenses separately.

Such an agreement should detail how rental income and expenses will be split to avoid discrepancies and comply with IRS regulations.It's essential for both cousins to adhere to IRS guidelines, which require accurate reporting of rental income and expenses based on ownership percentages.

Alternatively, you could also just apply a % annual appreciation based on historic data, but those typically won't give you the most accurate market data since they're averaged out across all/most property classes (e.g. a single family home may appreciate differently in your area than a mobile or multifam property, etc.) 

This is how you can keep the same system, same home layout, and just make a minor change to how the extra bedroom is filed with the cityAlthough not a pleasant surprise like you mentioned, luckily this is a very minor issue in reality and everything they're telling you is accurate.

So know your own numbers and never depend on wholesalers to provide accurate repair costs or ARVs. 

While specific rental data might be scarce on platforms like Rentometer, local real estate agents, property managers, and online rental listings can provide more accurate rent rates and market trends.

Anyway what you say is not accurate.