It is really good to have a capable head of the family who can support their kids with a good amount of money for investment. This may be a big risk but since those sold cows can be replaced once the other cows give birth. @OP you are lucky to have such a family. Many are struggling to get even $50 to invest in Bitcoin.
Dunno if this is a genuine post or another cook up story to attract merits, but I'm going to say this to you anyways. In as much as I'm pro Bitcoin, I would not advice anyone to sell his/her valuable properties in order to invest in Bitcoin. It's volatile asset and your investment could appreciate or plummet. Also, Bitcoin investment is not a get rich quick scheme, and it take time.
If you look at the Bitcoin price chart, Bitcoin had been a profitable business except to those who bought past the current Bitcoin price but we all know that the upcoming market bull run will possibly surpass the current ATH and that will give these investors to gain profit in their venture. Aside from that, in the case where new cows is coming since @OP stated that some of their cows will giving birth soon, it is a common action to sell the older cows in order to gain profit and at the same time minimize their maintainance when the new cows are delivered.
Do you even have knowledge of the market? Do you think your dad will be patient enough to wait for the value of Bitcoin to appreciate in order to take profit?
I think this is not our concern, since @OP is the one who does the convincing, he knows better. His money, his right to invest wherever @OP wanted. And invsting Bitcoin in this current time is I think profitable once Bitcoin start to break its ATH.
I bellieve @OP's father is patient enough since growing cows takes time before profit is seen. If anyone understands how patience is needed in an investment, I believe @OP's father knows it more than us.