Sounds like you are on the right tract and filed. Usually it gets ugly before it gets better. Keep civil and a business like situation. ALWAYS use text, email, or registered letters for communication or send one of those after a conversation takes place.
You are going to have to be patient and let the courts deal with her and make a schedule for when you have kids. Does the 14 year old want to visit you? Does this child have a cell phone, facebook page, other communication to communicate with child?
Once school is back in session, get on their mailing list, email teachers and ask when special things are going on. Use coaches, leaders, teachers, doctors office, dental office to get information instead of your ex for now.
The GAL is a voice for both the KIDS. It is the KIDS lawyer, the you can have a lawyer and so can mom. The GAL should go and see kids with her and with you. They are supposed to talk to teachers, family, friends and see what is the best schedule for the children. You may want to ask for court ordered therapy with YOU and kids to repair relationship. GO interview some, and find a therapist that will work for YOU and the KIDS and then ask the judge to order therapy. If their is a GAL assigned, call them, respectful ask how they work things and make appointment to see GAL (with or without kids). Just tell GAL over and over "just want to have a working parenting relationship with their mother in order for me to be in their life and have regular parenting time. Some GAL's are good, many are not and overworked. Ask if the GAL can make a temporary schedule to see kids this summer until the next court date. Sometimes they will act inbetween parents. TAKE ANY time that is offered.
Keep asking for time with kids and document. Text ex "I would like to see the kids this week, please let me know which night would be good for me to take them after work until 8pm. Thank you" Call/leave ONE voice message "Calling to talk to kids and see how their day went, please have them call me back before bed tonight". If you over text/call she could claim harassment so be careful until court. You can add to the
court order many things such as times for phone calls with kids, exact times, days, places for pick ups and drop offs, summer visits, holidays with times, school vacations, your birthday, their birthdays... Look at some detailed parenting plans on this site. If it is not in your court order, you do not have it. If is is vague with no times/days your ex can argue so get it detailed as possible but take what you can get for now if she offers.