How to resample data to monthly on 1. not on last day of month?

Question

I have daily price data on Bitcoin and the USD/EUR. I resampled them to monthly data by

usd_df_m = usd_df.resample("M", on="Date").mean()

df_months = df.resample("M", on="Date").mean()

I also got data on the monthly federal funds rate. I tried to merge all three monthly data frames by

monthly_merge = df_months.merge(usd_df_m,on='Date').merge(int_df,on='Date')

The problem is that the int_df looks like this:

and the Bitcoin df and USD df looks like this:

So how would you solve this if one df takes the first of a month and the other always take the last of a month?