A lot of effort is expended to protect the mailand from pests, undesireable plant materials and related items found in Hawaii. It is best to not take materials back at all. If you have specific interests and really want to do so, here are the rules as I understand them.

Taking plants to the mainland is controlled by the Federal Dept of Agriculture. Your brother can buy some variety of precertified plants from the airports, ABC stores and specialty stores.

He can also take back plants that have been prepared for shipping, with all the shipping and packing materials to the local Federal Dept of Agriculture. After they have been bare rooted and cleaned, you can hope they will pass them. They will not pass all plants. It is a lot of work for plants that will probably not make it in Pennsylvania. and even with all of this, there is some danger of bringing undesireable materials to your home.