It's written on the website pasted below that when tout modifies a feminine adjective beginning with a consonant sound or an aspirated h, it must take the form toute irrespective of whether the adjective is singular or plural. https://french.kwiziq.com/revision/grammar/tout-tous-and-toute-toutes-all-all-of-them-the-whole-indefinite-pronouns
Hence, it translates Elles sont toutes joyeuses as "They are all merry" (toutes used as a pronoun) and Elles sont toute joyeuses as "They're very merry" (toute used as an adverb). However, the following website states that tout has to agree both in gender and number with the feminine adjective (beginning with a consonant or an aspirated h) that follows it. And it translates Elles sont toutes petites as "They're very small". https://www.fluentu.com/blog/french/tout-vs-tous/
So, which one is correct? I don't think both of them can be acceptable.