Cloud Based Coin Collection/Inventory Software

I can put spreadsheets in Google Drive which I can access from anywhere, including my phone. The Sheets app on Android opens the files just fine.

Two "cloud" based collection management sites that you may want to consider are Heritage Auctions My Collection and Whitman Publishing My Collections. You have to create a free account to use either one. The Heritage account would also let you bid on/purchase items and get access to historical prices realized. Many (most?) CCF members have Heritage accounts for these reasons.

Here's a screenshot of the Heritage input form

and here's a screenshot of the Whitman input form


Both of these sites can either be private or public. You could share the userid and password between yourself and your father and both of you would have access to your collection information.

I don't keep my collection information in either site, but have put a few test coins into both just to see how they work. Both of them seemed acceptable and pretty comprehensive. Each also provides pricing data, which probably isn't up to the minute but should at least be in the ball park if you're interested. I can't comment on how secure they are, but if you're just entering generic, non-identifying information into them then I wouldn't think this would be an issue even if they were compromised.