I believe I have the best/easiest method for the donating achievements
You don't need to grind coins. Just use your coins to buy Dog coins and then save before starting
Turn 30 coins to 500 by just playing slots. Just spam A and you should earn more than you lose
If somehow you run out of coins you can dashboard and reload your save to retry
In Video at 36:00 - Dognation 1-7: 39:30
Achievement Walkthrough: