A weedkiller should not be used in this case because you have other
plants nearby that the chemicals may affect.
Because I am not sure (a) just how big this monster ivy is, (b) how much of a root system it has already developed and (c) do not know if the three
plants root systems are intertwined, I will suggest that you be "somewhat nice" to the ivy.
Rather than pulling ivy stems off the ground and finding that the ivy roots are intertwined with the roots of the other
plants, try cutting the ivy stems near the ground and let them be until they dry out.
You can then separate the
plants above ground or wait until the ivy has browned out. Use good pruners to facilitate this process.
In the future, if you see new leaves from the ivy, cut them immediately. You want to prevent it from
growing new leaves. It is a very slow process but eventually, the ivy will die. It will also be safe for the other
plants and their roots.
As for adding fertilizers and stuff, I would hate to comment since you do not know what one of the
plants is. Certain shrubs should not be fed any more fertilizer beginning in the summer because all growth needs to be winter-hardy by the Fall. So, if they really look as bad as you say, Liquid Seaweed (works as foliar food too) would be the most I would recommend for a little while; follow label directions. Do not go overboard since this organic fertilizer will also be feeding the ivy's roots.
That is my suggestion. Good luck, emmarose!