Higher downpayment - helps or hurts for a long turn investment?

[Emily Wilson]

First time investor here.  We are only getting into this market because we are trying to help a family member, but we would like the plan to help our future too.  Original idea - buy a duplex in Sacramento, CA with 25% downpayment (which we have). Elderly grandmother would live in 1/2 for a reduced rent and the rent of the other half would subsidize the payments for aprox. 5-8 years.  The idea was just to break even while taking care of my grandma.  However, the hope that is through CA real estate, we would be gaining equity with increased home value and when my relative is no longer with us, we would be able to rent both sides and actually make a profit. 

Unfortunately, the prices compared to the rents don't quite make the numbers work with this idea, since my grandma has such a low fixed income and can contribute so little.  Anytime there is something that fits the bill, it is snapped up in less than 24 hours.  

There are not many available, but there are a few small SFH that are a little over 1/2 of the price of the duplex. If we put down the same money we saved for the downpayment, it would be about 50% downpayment instead of 25%. There won't be many where we can get the ratio just right for my grandma, but if prices dip just a little, I think we can find something that works.

However, it occurred to me that as a person who is new to buying an investment property, are there downsides to having a 50% downpayment in terms of taxes, write-offs etc.?  I wonder if anyone has some insight into the financial considerations for these 2 scenarios?

Thanks