I can certainly understand your hesitation with regards to the weather, and unfortunately no-one can give any guarantees. I have, however, just looked at the weather in Budapest that week for the past two years. In 2018 the weather was gorgeous with sunny days, no rain and daily highs in the mid teens throughout. In 2017 there was one day of rain and temperature were in the low teens (and on a couple of days just reached 9 degrees). But by and large that is decent weather. Obviously that may change this year, but hopefully that gives you some information to go on.