Beginning to use a new thought

I have been working on allowing myself to feel emotions, specifically fear, panic and sadness regarding death – the death of my parents (future) and myself. When seeing them or thinking of time we’ve spent together (like the recent holidays) my brain reminds me that they are both mid-60s and that they could die soon and my time with them is limited. For example, I was looking at a gift I received at Christmas last night and the thought I immediately had was “This may have been our last Christmas together”. Or last night I was at my parent’s and my Mom received DVD copies of VHS tapes her Mom had made when she used to visit us and one of them was my Grandma’s 65th birthday. My thought immediately was “My Mom is now 65 I’m going to lose her soon”. I received some coaching on it yesterday and worked most of yesterday in allowing it and describing it as it came in waves, as well as being aware of the different thoughts that were producing the feeling of fear (they are similar, but not always the exact same like described above). I noticed that much of my dreams last night were about death and I assume that’s not surprising. This morning the waves of fear began again and as I was practicing allowing it two new thoughts came into my mind that caused the most profound feeling of peace – “I am glad my parents are alive” and “I am glad I am alive”. My question is, now that I have these thoughts (I’ve been working on my own since August on these thoughts and feelings, on my own and supplemented with the podcast and never found a thought I believed that made me feel better), can I begin to tell myself to use it when the original thoughts causing fear come up or would that be resisting the fear and thoughts that bring it? I want to make a new neural pathway where, when my brain goes to the fearful thoughts I can replace them with these, but I also understand that we’re taught not to rush the process. Thank you in advance for your time and advice.