In Russian:

The rule is that б/в/г/д/ж/з is pronounced like п/ф/к/т/ш/с if it appears before ч/х/ц/щ/п/ф/к/т/ш/с or at the end of a word, right?

In Ukrainian:

The rule is that б/в/ґ/д/ж/з is always pronounced like б/в/ґ/д/ж/з, right?